Date: Sat, 5 Aug 2023 00:48:28 +0200 From: Yuri <yuri@aetern.org> To: hackers@freebsd.org Subject: amd64-gcc12 seems to break linker sets Message-ID: <6a0f626c-95b4-2398-0a6d-9428c440131b@aetern.org>
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I noticed that kernel built using amd64-gcc12 panics on `kldload dtraceall`:
panic: probe defined without a provider
cpuid = 4
time = 1691186663
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x35/frame
0xfffffe00c448b8a0
vpanic() at vpanic+0x232/frame 0xfffffe00c448b950
panic() at panic+0x3c/frame 0xfffffe00c448b9b0
sdt_kld_load_probes() at sdt_kld_load_probes+0x346/frame 0xfffffe00c448bb70
sdt_load_probes_cb() at sdt_load_probes_cb+0x9/frame 0xfffffe00c448bb80
linker_file_foreach() at linker_file_foreach+0x53/frame 0xfffffe00c448bbc0
linker_load_dependencies() at linker_load_dependencies+0xe18/frame
0xfffffe00c448bc70
link_elf_load_file() at link_elf_load_file+0x10c6/frame 0xfffffe00c448bd50
sys_kldload() at sys_kldload+0x820/frame 0xfffffe00c448bdf0
amd64_syscall() at amd64_syscall+0x11b/frame 0xfffffe00c448bf30
fast_syscall_common() at fast_syscall_common+0xf8/frame 0xfffffe00c448bf30
--- syscall (304, FreeBSD ELF64, kldload), rip = 0x7e7e919615a, rsp =
0x7e7e70ef498, rbp = 0x7e7e70efa10 ---
Looking into it, gcc12 seems to discard the __start_set_... and
__stop_set_... symbols declared in sys/linker_set.h as __WEAK(), i.e.
__asm__(".weak ...").
The following small test shows the problem:
---
int
main(void)
{
return (0);
}
__asm__(".weak __start_set_sdt_providers_set");
static void const * const __set_sdt_providers_set_sym_sdt_provider_tst
__attribute__((__section__("set_" "sdt_providers_set")))
__attribute__((__used__)) = &(main);
__asm__(".weak __stop_set_sdt_providers_set");
---
When built using system clang:
---
$ cc -c -o t.o t.c; nm t.o
0000000000000000 r __set_sdt_providers_set_sym_sdt_provider_tst
w __start_set_sdt_providers_set
w __stop_set_sdt_providers_set
0000000000000000 T main
---
When built using amd64-gcc12:
---
$ /usr/local/bin/x86_64-unknown-freebsd14.0-gcc12 -c -o t.o t.c; nm t.o
0000000000000000 r __set_sdt_providers_set_sym_sdt_provider_tst
0000000000000000 T main
---
I haven't found any options to tell gcc to stop doing that; any hints?
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