Bug 250992 - Binaries produced by clang -pg on x86-64 always crash in ld-elf.so.1
Summary: Binaries produced by clang -pg on x86-64 always crash in ld-elf.so.1
Status: New
Alias: None
Product: Base System
Classification: Unclassified
Component: bin (show other bugs)
Version: 12.2-RELEASE
Hardware: amd64 Any
: --- Affects Only Me
Assignee: freebsd-toolchain (Nobody)
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2020-11-09 20:40 UTC by Oleg Derevenetz
Modified: 2020-11-13 02:08 UTC (History)
3 users (show)

See Also:


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Description Oleg Derevenetz 2020-11-09 20:40:52 UTC
Consider the following program (test.c):

$ cat test.c
#include <stdio.h>

int main()
{
    printf("OK\n");
}

When built using the following command:

$ clang -pg test.c

the following binary is produced:

$ file a.out
a.out: ELF 64-bit LSB executable, x86-64, version 1 (FreeBSD), statically linked, interpreter /libexec/ld-elf.so.1, for FreeBSD 12.2, FreeBSD-style, with debug_info, not stripped

(note the "interpreter /libexec/ld-elf.so.1" part).

Once launched, it crashes inside ld-elf.so.1 with SIGSEGV:

$ lldb a.out
(lldb) target create "a.out"
Current executable set to '/usr/home/oleg/tmp/pg/a.out' (x86_64).
(lldb) run
Process 872 launching
Process 872 launched: '/usr/home/oleg/tmp/pg/a.out' (x86_64)
Process 872 stopped
* thread #1, name = 'a.out', stop reason = signal SIGSEGV: invalid address (fault address: 0x0)
    frame #0: 0x00000008002a3ab0
->  0x8002a3ab0: movq   (%r15), %rdx
    0x8002a3ab3: cmpq   $0x6fffffef, %rdx         ; imm = 0x6FFFFFEF
    0x8002a3aba: jg     0x8002a3b10
    0x8002a3abc: cmpq   $0x21, %rdx
(lldb) disassemble
->  0x8002a3ab0: movq   (%r15), %rdx
    0x8002a3ab3: cmpq   $0x6fffffef, %rdx         ; imm = 0x6FFFFFEF
    0x8002a3aba: jg     0x8002a3b10
    0x8002a3abc: cmpq   $0x21, %rdx
    0x8002a3ac0: ja     0x8002a3ba6
    0x8002a3ac6: movslq (%r12,%rdx,4), %rax
    0x8002a3aca: addq   %r12, %rax
    0x8002a3acd: jmpq   *%rax
(lldb)

Disassembled code above is apparently from ld-elf.so.1/_rtld_is_dlopened.

However, if the following command is used for the build:

$ clang -pg -static test.c

the following binary is produced:

$ file a.out
a.out: ELF 64-bit LSB executable, x86-64, version 1 (FreeBSD), statically linked, for FreeBSD 12.2, FreeBSD-style, with debug_info, not stripped

(note the absence of "interpreter ..." part). This binary runs just fine:

$ lldb a.out
(lldb) target create "a.out"
Current executable set to '/usr/home/oleg/tmp/pg/a.out' (x86_64).
(lldb) run
Process 914 launching
Process 914 launched: '/usr/home/oleg/tmp/pg/a.out' (x86_64)
OK
Process 914 exited with status = 0 (0x00000000)
(lldb)
Comment 1 Konstantin Belousov freebsd_committer 2020-11-09 21:33:00 UTC
This is a bug in lld.  There was similar bug report recently, I cannot find
its number.
Comment 2 Oleg Derevenetz 2020-11-09 22:18:57 UTC
I found similar bug report in LLVM bugtracker:

https://bugs.llvm.org/show_bug.cgi?id=47455

with some discussion. According to truss output, the -dynamic-linker flag is actually being passed to lld:

  890: execve("/usr/bin/clang",[ "/usr/bin/clang", "-cc1", "-triple", "x86_64-unknown-freebsd12.2", "-emit-obj", "-mrelax-all", "-disable-free", "-disable-llvm-verifier", "-discard-value-names", "-main-file-name", "test.c", "-mrelocation-model", "static", "-mthread-model", "posix", "-mframe-pointer=all", "-fno-rounding-math", "-masm-verbose", "-mconstructor-aliases", "-munwind-tables", "-target-cpu", "x86-64", "-dwarf-column-info", "-fno-split-dwarf-inlining", "-debugger-tuning=gdb", "-resource-dir", "/usr/lib/clang/10.0.1", "-fdebug-compilation-dir", "/usr/home/oleg/tmp/pg", "-ferror-limit", "19", "-fmessage-length", "237", "-pg", "-fgnuc-version=4.2.1", "-fobjc-runtime=gnustep", "-fdiagnostics-show-option", "-fcolor-diagnostics", "-faddrsig", "-o", "/tmp/test-63e2c7.o", "-x", "c", "test.c" ],0x7fffffffebb0) EJUSTRETURN
  891: execve("/usr/bin/ld",[ "/usr/bin/ld", "--eh-frame-hdr", "-dynamic-linker", "/libexec/ld-elf.so.1", "--hash-style=both", "--enable-new-dtags", "-o", "a.out", "/usr/lib/gcrt1.o", "/usr/lib/crti.o", "/usr/lib/crtbegin.o", "-L/usr/lib", "/tmp/test-63e2c7.o", "-lgcc_p", "-lgcc_eh_p", "-lc_p", "-lgcc_p", "-lgcc_eh_p", "/usr/lib/crtend.o", "/usr/lib/crtn.o" ],0x7fffffffebb0) EJUSTRETURN

However, it's unclear to me, why it is passed in the first place, if clang -pg wants to produce statically linked binary. There is apparently some inconsistency.