Guard ABSL_HAVE_ELF_MEM_IMAGE on <link.h> availability, not a deny-list - #2156
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Guard ABSL_HAVE_ELF_MEM_IMAGE on <link.h> availability, not a deny-list#2156afonsojanu wants to merge 1 commit into
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Any __ELF__ target without a real dynamic loader has no <link.h>, and this header unconditionally includes it once ABSL_HAVE_ELF_MEM_IMAGE is turned on. Bare-metal ELF toolchains such as arm-none-eabi-g++ with newlib produce ELF objects but never ship link.h, so the build fails with a fatal "link.h: No such file or directory" before it even gets to using anything from it. The existing guard tries to work around this with a deny-list of platforms (__QNX__, __asmjs__, __wasm__, __HAIKU__, __VXWORKS__, __hexagon__, __XTENSA__), each added one at a time as it hit the same wall. Every new bare-metal ELF target has to send its own PR to add itself to the list. Added a __has_include(<link.h>) check alongside the existing guard, so the feature is only enabled where the header it depends on actually exists, rather than only where we remembered to exclude. Kept a fallback for preprocessors that predate __has_include.
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Fixes #2153.
ABSL_HAVE_ELF_MEM_IMAGEis turned on for every__ELF__target except an explicit deny-list, and once it's on,elf_mem_image.hunconditionally includes<link.h>. That header is a glibc/dynamic-linker thing, not part of the ELF format itself, so any bare-metal ELF toolchain without a real dynamic loader (the reported case isarm-none-eabi-g++with newlib) hits a fatallink.h: No such file or directorybefore compilation even gets to using anything from it.The deny-list (
__QNX__,__asmjs__,__wasm__,__HAIKU__,__VXWORKS__,__hexagon__,__XTENSA__) is really just a running list of platforms that hit this one at a time, each needing its own PR to add itself.Added
__has_include(<link.h>)to the guard so the feature turns on based on whether the header it needs is actually there, with a fallback for preprocessors that don't support__has_include(there's already a precedent for this inabsl/base/config.h).Verified two ways since I don't have the reporter's exact
arm-none-eabi-g++/newlib setup handy:link.h: the current code reproduces the exact reported error, the fix compiles clean and simply doesn't defineABSL_HAVE_ELF_MEM_IMAGE.link.hpresent on the include path: confirms the fix still definesABSL_HAVE_ELF_MEM_IMAGEand includes the header, so real ELF/glibc targets are unaffected.I didn't touch the deny-list itself, it's harmless now (each of those platforms also lacks
link.h, so the new check alone would already exclude them), but removing it felt like a separate cleanup from the actual bug fix.