Apache httpd

Author: Ludovic HENRY ludovic.henry@qti.qualcomm.com
Date: 2026-06-17
Scope: RISC-V (riscv64/linux) support status for Apache httpd
Audience: Technical leadership, resource allocation strategy
Verification policy: Every claim is cross-referenced to a primary upstream source. Items that could not be verified against a second source are marked [NEEDS VERIFICATION].

1. Project Overview

Apache httpd is the Apache HTTP Server, a general-purpose HTTP server maintained by the Apache Software Foundation (ASF). It is one of the most widely deployed web servers on the public internet. The project is governed by a PMC (Project Management Committee) of 57 listed members under the standard ASF lazy-consensus model. Decisions are made via mailing lists. The primary source repository is SVN; the GitHub repository at apache/httpd is a mirror. The project’s primary bug tracker is ASF Bugzilla. License: Apache License 2.0.

PMC Chair: Joe Orton (jorton), Red Hat.

No formal corporate sponsorship exists for the httpd project specifically. ASF-level platinum sponsors include Apple, Amazon Web Services, Meta, Google, Huawei, Microsoft, Snowflake, and VISA.

Top active committers by commit count in the last 100 commits on the GitHub mirror:

Committer Commits Affiliation
Rich Bowen (rbowen) 42 Red Hat / IBM
Joe Orton (jorton) 22 Red Hat
Rainer Jung (rainerjung) 10 –
Lucien Gentis (lgentis) 9 –
Jim Jagielski (jimjag) 7 –
Eric Covener (covener) 6 IBM

2. Port History and Upstreaming Timeline

Apache httpd has no RISC-V port history in its upstream repository. Searches across the GitHub mirror returned zero results for “riscv” or “riscv64” across issues, pull requests, commits, and code. There is no first RISC-V commit to report.

The project contains no architecture-specific code at any level. The httpd os/ directory contains only: unix/, win32/, os2/, netware/, bs2000/. No riscv/ or riscv64/ subdirectory has ever existed. The modules/arch/ directory contains only OS-level modules: unix/, win32/, netware/.

The STATUS file in the repository lists OS/2 and NetWare support as candidates for removal, indicating the project actively prunes unused platform support rather than adding new tiers.

riscv64 works without a port because httpd is pure portable C with no CPU-ISA-specific code paths. All architecture-sensitive functionality (atomics, thread primitives) is delegated to APR (Apache Portable Runtime), which handles riscv64 correctly via GCC __atomic_* compiler intrinsics.

The APR repository (apache/apr) also contains zero references to “riscv” or “riscv64”. APR falls through to its builtins.c / builtins64.c implementation on riscv64, the same path used by arm64.

3. Upstream Support Tier

Apache httpd does not publish a formal tiered-support policy document (no PLATFORMS.md, SUPPORT.md, or docs/platforms/ in the repository). README.platforms covers Darwin, FreeBSD, HP-UX, AIX, Solaris, and Ubuntu – no RISC-V mention.

riscv64 is not listed as a supported, unsupported, or experimental target by the upstream project. The upstream project has no position on riscv64 at all.

De-facto support status, based on distribution evidence: riscv64 builds successfully and is treated as a first-class architecture by both Debian and Ubuntu packaging teams. The upstream project is unaware of this because no issues, patches, or CI work has been contributed upstream.

4. Technical Architecture and RISC-V-Specific Subsystems

Apache httpd is a pure-C POSIX server. It has no JIT, no SIMD dispatch, no inline assembly, and no architecture-specific code paths anywhere in the source tree. The following audit was performed against the trunk tree:

  • modules/ssl/ – pure C, no assembly
  • modules/http2/ – pure C, no assembly
  • modules/filters/ – pure C, no assembly
  • server/ – no .S files, no arch-specific C
  • build/ – build system covers AIX, NetWare, Win32 only
  • acinclude.m4 – no riscv references
  • configure.in – no riscv references; platform list: OS/2, Linux, BSD, Solaris, Cygwin, MinGW, AIX, OS/390, Darwin

Code search for #ifdef __riscv in apache/httpd: 0 matches.

All crypto and compression SIMD acceleration is delegated to external libraries (OpenSSL, zlib, brotli). Those libraries handle their own architecture dispatch internally and are out of scope for the httpd source tree.

APR atomics on riscv64

The only architecture-specific layer that httpd depends on is APR’s atomic operations. APR’s include/arch/unix/apr_arch_atomic.h selects an implementation by cascading through architecture checks. There is no riscv.c or riscv64.c in APR. On riscv64 with GCC >= 4.7 or Clang >= 3.1, APR detects HAVE__ATOMIC_BUILTINS at configure time and selects builtins.c / builtins64.c.

builtins.c correctly identifies riscv64 as a weak-memory-ordering architecture:

#if defined(__i386__) || defined(__x86_64__) \
    || defined(__s390__) || defined(__s390x__)
#define WEAK_MEMORY_ORDERING 0
#else
#define WEAK_MEMORY_ORDERING 1   // riscv64 lands here
#endif

With WEAK_MEMORY_ORDERING 1, all atomic operations use __ATOMIC_SEQ_CST ordering, which is correct for RISC-V’s weak memory model. The implementation is not a stub. arm64 (AArch64) is in the same category and is considered fully supported by the project.

Architecture-specific file count comparison (APR + httpd combined):

Architecture Dedicated arch files (httpd) Dedicated APR atomic files Total
amd64 / x86_64 0 1 (ia32.c, hand-tuned inline asm) 1
arm64 / aarch64 0 0 (uses builtins.c) 0
PowerPC 0 1 (ppc.c, hand-tuned inline asm) 1
IBM S390 0 1 (s390.c, hand-tuned inline asm) 1
riscv64 0 0 (uses builtins.c) 0

The absence of a dedicated riscv64.c in APR is not a gap. amd64 has hand-tuned inline assembly for atomics; riscv64 and arm64 both rely on compiler intrinsics. The compiler intrinsic path is a complete, production-quality implementation.

5. Build System, Cross-Compilation, and Toolchain

The CMake build (CMakeLists.txt) is Windows-only and experimental. All Linux and riscv64 builds use the autoconf path.

Standard native build:

./buildconf   # from SVN/git only; not needed for release tarballs
./configure \
  --prefix=/usr/local/apache2 \
  --with-apr=/path/to/apr \
  --with-apr-util=/path/to/apr-util \
  --enable-mods-shared=reallyall \
  --enable-mpms-shared=all
make -j$(nproc)
make install

Cross-compilation for riscv64

There is no upstream cross-compilation toolchain file for riscv64. The only documented cross-compilation procedure is from the Debian packaging team (debian/rules). A single known issue exists: the build system runs server/gen_test_char at build time, which must be compiled for the build host, not the target. The Debian workaround:

export CC=riscv64-linux-gnu-gcc
gcc -DCROSS_COMPILE server/gen_test_char.c -o server/gen_test_char
./server/gen_test_char > server/test_char.h
touch server/gen_test_char.lo

./configure \
  --host=riscv64-linux-gnu \
  --build=x86_64-linux-gnu \
  --with-pcre=/usr/bin/pcre2-config \
  CC=riscv64-linux-gnu-gcc

Known test suite issue in emulated/cross environments (documented in test/travis_before_linux.sh):

# non-x86 builds have an IPv6 configuration which breaks the test suite.
# Apache::Test only configures Listen on 0.0.0.0 but
# Apache::TestServer::wait_till_is_up() tries to connect via ::1.
if grep ip6-localhost /etc/hosts; then
    sudo sed -i "/ip6-/d" /etc/hosts
fi

This affects all non-x86 build environments including riscv64 QEMU VMs and native boards. IPv6 entries must be removed from /etc/hosts before running the test suite.

Minimum toolchain versions:

Component Minimum Reason
GCC (riscv64-linux-gnu-gcc) 7.1 First upstream RISC-V support (RV64GC, lp64d ABI)
binutils 2.28 First upstream RISC-V support
glibc 2.27 First upstream RISC-V port
APR 1.7.x or trunk (2.x) httpd trunk requires APR 2.0 or APR 1.7.x + APR-util 1.7.x
PCRE2 10.x (any) Required; --with-pcre2 or system libpcre2-dev
QEMU (emulated native) 2.12+ First QEMU with riscv64 virt machine complete enough for Linux
Linux kernel 4.15+ (4.19+ recommended) First kernel with upstream RISC-V port

No riscv64-specific --disable-X flags are required. The gen_test_char cross-compilation issue is the only known build-time workaround.

6. Feature Coverage and Gap Analysis vs arm64 and amd64

Component amd64 arm64 riscv64 Notes
APR atomic 32-bit ops hand-tuned inline asm (ia32.c) C intrinsics (builtins.c) C intrinsics (builtins.c) Functional parity; amd64 may have marginal latency advantage
APR atomic 64-bit ops hand-tuned inline asm (ia32.c) C intrinsics (builtins64.c) C intrinsics (builtins64.c) Same as above
APR mutex / locks POSIX pthreads POSIX pthreads POSIX pthreads Identical
httpd MPM (event/worker/prefork) pure C pure C pure C Identical
httpd connection handling pure C pure C pure C Identical
httpd module architecture OS-level only OS-level only OS-level only Identical
TLS (mod_ssl via OpenSSL) full hardware acceleration full hardware acceleration hardware acceleration requires Zkn or Zvkned; soft otherwise See section 9
Compression (mod_deflate via zlib) SIMD (SSE2/AVX512) SIMD (NEON) generic C only Performance gap, not correctness gap
Compression (mod_brotli via brotli) architecture-optimized architecture-optimized supported [NEEDS VERIFICATION] Brotli GitHub issue #669 (riscv64 support) is closed
HTTP/2 (mod_http2 via nghttp2) full full full No riscv64 issues in nghttp2
Pattern matching (mod_rewrite via PCRE2) JIT-accelerated (SLJIT) JIT-accelerated (SLJIT) JIT status unconfirmed [NEEDS VERIFICATION] SLJIT claims riscv64 support; no PCRE2 code hits for riscv64 in GitHub
Lua scripting (mod_lua) reference Lua interpreter reference Lua interpreter reference Lua interpreter httpd uses reference Lua (not LuaJIT); no JIT gap

Summary: For the httpd core and all standard modules, riscv64 is at feature parity with arm64. The two areas with a measurable gap are OpenSSL TLS acceleration (security-critical on hardware without scalar/vector crypto extensions) and zlib deflate throughput (performance only).

7. CI/CD Infrastructure

Apache httpd upstream CI has no riscv64 coverage.

The repository contains exactly two workflow files: .github/workflows/linux.yml and .github/workflows/windows.yml. Both were read in full. Neither contains any reference to “riscv”, “riscv64”, or QEMU-based cross-compilation. No .gitlab-ci.yml, Jenkinsfile, or .cirrus.yml exists in the repository.

Current upstream CI matrix:

Workflow Runner Architecture
linux.yml ubuntu-latest x86_64
linux.yml ubuntu-24.04-arm arm64
windows.yml windows-latest x64

There is no ubuntu-24.04-riscv64 GitHub Actions runner (none exists in GHA as of this report date), nor any QEMU-based riscv64 emulation job.

riscv64 builds are tested exclusively by downstream distribution infrastructure (Debian buildd, Ubuntu Launchpad). The Debian apache2 package is built on buildd host rv-osuosl-04, a native RISC-V machine at Oregon State University Open Source Lab. This is entirely outside the apache/httpd upstream CI.

8. Distribution and Release Status

Apache httpd upstream does not publish binary releases. The official download at httpd.apache.org/download.cgi provides only source tarballs (httpd-2.4.68.tar.bz2, httpd-2.4.68.tar.gz). Architecture-specific binary packaging is entirely delegated to downstream OS distributions.

Distribution Package name riscv64 available Version Build status
Debian Sid apache2 YES 2.4.68-1 Installed on buildd host rv-osuosl-04 (native RISC-V hardware at OSU OSL)
Ubuntu 24.04 Noble apache2 YES 2.4.58-1ubuntu8 .deb file apache2_2.4.58-1ubuntu8_riscv64.deb (90240 bytes); riscv64 listed as an officially supported architecture
Arch Linux RISC-V apache Likely YES [NEEDS VERIFICATION] – Not present in the archriscv FTBFS failure tracker; no positive .pkg.tar.zst URL confirmed
GitHub Releases (apache/httpd) – NO – No releases published; GitHub repo is source mirror only
PyPI (apache-httpd) – NO – HTTP 404; package does not exist

The distribution picture is strong. Both Debian Sid and Ubuntu 24.04 LTS carry current riscv64 binary packages built from standard packaging with no architecture-specific patches beyond the gen_test_char cross-compilation workaround.

9. Dependencies

All dependency build status data is sourced from Debian Sid buildd records and the relevant upstream issue trackers.

Dependency Role riscv64 build status Open riscv64 issues Notes
APR Core I/O, threading, memory pools – mandatory Installed (Debian Sid 1.7.6-3+b1) None No riscv-specific code; uses builtins.c GCC __atomic_* intrinsics. Functionally correct.
APR-Util APR extension: crypto, DBD, LDAP – mandatory with APR 1.x Installed (follows APR) None Merged into APR 2.x, removing separate dependency.
OpenSSL TLS for mod_ssl – production-essential Installed (Debian Sid 3.6.3-1) 2 open (1) AES T-table not constant-time on hardware without Zkn/Zvkned scalar crypto – security-critical for TLS. (2) SSL tests fail under high HARNESS_JOBS on riscv64. Cross-compile with no-deprecated also has an open issue.
PCRE2 URL pattern matching for mod_rewrite – mandatory Installed (Debian Sid 10.46-1+b2) None active JIT backend (SLJIT) claims riscv64 support [NEEDS VERIFICATION]. No riscv64 correctness bugs.
zlib gzip/deflate for mod_deflate – optional but common Installed (Debian Sid 1.3.dfsg+really1.3.2-3) None No riscv64 SIMD paths; generic C only. Performance gap vs x86/ARM. No correctness issue.
libbrotli Brotli compression for mod_brotli – optional Installed (Debian Sid 1.2.0-3) None GitHub issue #669 “Add RISC-V 64-bit (riscv64) platform configuration” is closed. Supported.
nghttp2 HTTP/2 for mod_http2 – optional Installed (Debian Sid 1.69.0-1) None Two historical riscv64 issues both closed (GCC 14 compile warning, m4 file update).
libcurl ACME/Let’s Encrypt for mod_md – optional Installed (Debian Sid) None All 10 riscv64 issues in curl/curl are closed; most were compiler warning suppressions.
libxml2 XML parsing for mod_proxy_html, mod_dav – optional Installed (Debian Sid 2.15.3+dfsg-1) None 0 riscv64 issues in GNOME/libxml2.
libjansson JSON for mod_md – optional Maybe-Successful older build; 2.15.0-1 queued None Needs-Build status is Debian buildd scheduling lag, not a code defect. 0 upstream riscv64 issues.
liblua5.4 Lua scripting for mod_lua – optional Installed (Debian Sid 5.4.8-1+b2) None Reference Lua interpreter only (not LuaJIT). No JIT gap. 0 riscv64 issues.
glibc C runtime – mandatory Installed Historical (fixed) Historical SIGILL bug for RVV prctl-disabled contexts in memset; fixed in 2.43.

The single dependency with active, security-relevant open upstream issues is OpenSSL. On riscv64 hardware without Zkn (scalar cryptography) or Zvkned (vector AES) extensions, OpenSSL’s AES implementation uses T-tables, which are not constant-time and are vulnerable to cache-timing attacks. This is a security-critical issue for any production httpd TLS deployment on riscv64 hardware lacking those extensions.

10. Ecosystem Status

RISE Project involvement: None. Apache httpd is not a member project, has no RISE RFP, and has received no RISE blog coverage. A review of all 27 RISE blog posts from May 2024 through June 2026 found zero mentions of Apache httpd. The RISE RFP list (RP001-RP016) has no httpd entry. The term “apache” appears in RISE content only in the phrase “Apache 2.0 license” in a post about Python wheels (RP011).

RISE Premier Members include Andes Technology, Google, MediaTek, NVIDIA, Qualcomm, Red Hat, SiFive, DAMO Academy (Alibaba), and Tenstorrent. The RISE project’s focus is on compilers (LLVM/GCC), language runtimes (Go, Rust, Java, Python, V8), AI/ML (PyTorch, llama.cpp), firmware (EDK2, OpenSBI), and CI infrastructure.

Community activity on riscv64: Zero. There are no mailing list threads, no GitHub issues, no PRs, and no commits in the upstream repository related to riscv64. The architecture works without intervention, so it has attracted no community discussion.

11. Known Bugs and Active Issues

Apache httpd (upstream): No riscv64-specific bugs found. The GitHub repository contains zero issues or PRs mentioning riscv64. ASF Bugzilla required authentication and could not be searched; a residual uncertainty exists, but given the clean Debian/Ubuntu build record, active riscv64-specific bug reports are unlikely.

Dependency issues affecting riscv64 httpd deployments:

Issue Component Severity Status
AES T-table not constant-time on hardware without Zkn/Zvkned OpenSSL Security-critical for TLS serving Open
SSL tests fail under high HARNESS_JOBS OpenSSL Test infrastructure Open
Cross-compile with no-deprecated fails OpenSSL Build Open
IPv6 test suite failure in non-x86 environments Apache httpd test infrastructure Test infrastructure only Known workaround exists (documented in travis_before_linux.sh)

No correctness bugs are known for the httpd core itself on riscv64. The OpenSSL TLS issue is the only security-relevant open item in the dependency chain.

12. Objections and Upstream Blockers

There are no upstream blockers for riscv64 httpd deployment. The following objections are pre-empted by existing evidence:

“APR does not support riscv64”: Incorrect. APR falls through to builtins.c on riscv64, which uses GCC __atomic_* intrinsics with __ATOMIC_SEQ_CST ordering. This is correct for RISC-V’s weak memory model. Debian Sid libapr1 builds and installs on riscv64 without issue.

“httpd requires a port to build on riscv64”: Incorrect. httpd contains zero architecture-specific code. It is pure portable C. No port work has ever been needed or done.

“No upstream CI means the build is untested”: Partially true. The upstream CI has no riscv64 coverage. However, the Debian buildd infrastructure (native riscv64 hardware at OSU OSL) provides continuous integration for every upload, which covers all production-relevant configurations. Upstream CI gaps are a documentation and trust-surface issue, not a functional one.

“LuaJIT is missing on riscv64”: Not relevant to httpd. mod_lua uses the reference Lua 5.4 interpreter, not LuaJIT. This is distinct from nginx+OpenResty, which depends on LuaJIT.

“PCRE2 JIT is unconfirmed on riscv64”: True but bounded. PCRE2 operates in interpreter mode when JIT is unavailable. This is a performance regression for heavy mod_rewrite workloads, not a correctness issue.

13. Investment Analysis

13.1 Functional Enablement

No functional enablement work is needed. Apache httpd builds, packages, and runs on riscv64 today. Debian Sid and Ubuntu 24.04 LTS carry current binary packages. The gen_test_char cross-compilation workaround is already documented and handled by Debian packaging.

The only functional gap requiring attention is in the dependency layer: OpenSSL AES constant-time behavior on hardware without Zkn/Zvkned. This issue is in the OpenSSL project, not in httpd.

13.2 Performance Optimization

Performance data for Apache httpd specifically on riscv64 does not exist in any publicly accessible source (no benchmarks found in the RISE blog, GitHub, or web search). The available riscv64 performance context is indirect: RISE RP009 (LLVM SPEC CPU 2017, May 2025, SpacemiT-X60) showed up to 15.7% reduction in SPEC CPU execution time from compiler scheduling model improvements. This is a compiler benchmark, not an httpd benchmark.

Known performance gaps vs arm64 and amd64:

  1. zlib deflate (mod_deflate): riscv64 runs generic C. amd64 uses SSE2/AVX512; arm64 uses NEON. This is a throughput gap for compression-heavy workloads. The fix is in zlib, not httpd.
  2. OpenSSL AES (mod_ssl): On hardware without Zkn/Zvkned, AES runs on the T-table software path, which is slower and not constant-time. The fix is in OpenSSL + hardware provisioning.
  3. PCRE2 JIT (mod_rewrite): JIT status on riscv64 is unconfirmed. If disabled, mod_rewrite pattern matching runs the interpreter. The fix is in PCRE2/SLJIT.

None of these gaps require work in the httpd repository itself.

13.3 CI/CD Infrastructure

The upstream CI gap (no riscv64 runner or QEMU job) is the highest-value improvement available within the httpd project. Adding riscv64 to the upstream CI matrix would:

  • Catch regressions before they reach distributions
  • Signal upstream support commitment to the community
  • Reduce reliance on downstream Debian buildd as sole gating infrastructure

GitHub Actions does not currently offer a hosted ubuntu-24.04-riscv64 runner. A riscv64 CI job would require either a self-hosted RISC-V runner or a QEMU-based job. The test suite IPv6 workaround (removing ip6-localhost from /etc/hosts) is already documented and must be applied in any non-x86 CI environment.

13.4 Ecosystem Enablement

Apache httpd has no RISE project involvement and no community activity around riscv64. This is not a gap requiring remediation – it reflects that the project works without intervention. Ecosystem work (RISE RFP proposal, blog post, CI contribution) would be primarily a visibility exercise, not a technical necessity.

13.5 Summary Table

Area Work Item Effort (person-weeks) Owner Priority
Functional None required – httpd builds and runs on riscv64 today 0 – –
Functional (dependency) OpenSSL AES constant-time fix on riscv64 without Zkn/Zvkned ~4-8 (in OpenSSL, not httpd) OpenSSL maintainers High (security-critical for TLS deployments)
CI/CD Add riscv64 QEMU CI job to upstream linux.yml 1-2 httpd PMC contributor Medium
CI/CD Self-hosted native riscv64 runner for upstream httpd CI 2-4 (infra setup) ASF infra or chip vendor Medium
Performance zlib SIMD for riscv64 (RVV deflate path) ~4-8 (in zlib, not httpd) zlib maintainers Low (no correctness impact)
Performance PCRE2 SLJIT JIT verification on riscv64 1 PCRE2 maintainers Low
Documentation Document riscv64 cross-compilation in upstream INSTALL or README.platforms 0.5 httpd PMC contributor Low
Ecosystem RISE RFP proposal for httpd riscv64 CI 1 Chip vendor / ASF Low

14. Updates

No updates yet – initial report dated 2026-06-17.

15. References