fix(build): avoid jt9 SIGSEGV from gfortran stack trampolines - #53
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fix(build): avoid jt9 SIGSEGV from gfortran stack trampolines#53cjkjellander wants to merge 1 commit into
cjkjellander wants to merge 1 commit into
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gfortran compiles the FT8 decoder callback (an internal procedure passed as an actual argument) into a trampoline placed on the stack. Combined with the -Wa,--noexecstack hardening this crashes at run time (jt9 SIGSEGV in ft8_decode) on gfortran and hardened toolchains, because the trampoline cannot execute on a non-executable stack. Prefer heap-allocated trampolines when the compiler supports them (gfortran >= 14, -ftrampoline-impl=heap), which keeps the stack non-executable. On older compilers that lack the option, mark the stack executable so the trampoline runs instead of crashing.
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On Linux,
jt9segfaults insideft8_decode(SIGSEGV) with gfortran andhardened toolchains. The FT8 decoder callback is an internal procedure passed
as an actual argument, which gfortran implements as a trampoline placed on
the stack. The
-Wa,--noexecstackhardening added for certain Linux buildsmarks the stack non-executable, so the trampoline can no longer run and the
process crashes as soon as a decode is produced.
This is a build-time-vs-run-time trade-off:
noexecstackkeeps strict linkershappy but breaks the decoder at run time; an executable stack runs but trips a
linker warning on hardened distros.
The clean resolution is to stop putting the trampoline on the stack at all.
gfortran 14 added
-ftrampoline-impl=heap, which allocates trampolines on theheap and lets the stack stay non-executable. This PR:
-ftrampoline-impl=heapwithcheck_fortran_compiler_flag;-Wa,--noexecstack(no crash, no warning, stack stays non-executable);
-Wa,--execstackso thetrampoline can run, rather than crashing.
The fallback re-introduces the non-fatal
ld: warning: ... requires executable stackon older compilers — that is the correct trade-off (a warning beats arun-time crash), and modern toolchains avoid both paths.
Verified on gfortran 13.3 (Ubuntu 24.04): without this,
jt9'sGNU_STACKisRWand it SIGSEGVs inft8_decode; with the fallback it isRWEand decodingworks. gfortran >= 14 selects the heap-trampoline path.