Re: build failure on ia64 (+ patch), "relocation truncated to fit: GPREL22 against `.text'"

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 30/07/23 05:10, Florian Weimer wrote:
> * Andreas K. Huettel via Libc-alpha:
> 
>> diff --git a/sysdeps/unix/sysv/linux/ia64/dl-sysdep.h b/sysdeps/unix/sysv/linux/ia64/dl-sysdep.h
>> index 3e4d5da820..eb7681b704 100644
>> --- a/sysdeps/unix/sysv/linux/ia64/dl-sysdep.h
>> +++ b/sysdeps/unix/sysv/linux/ia64/dl-sysdep.h
>> @@ -32,7 +32,9 @@
>>  #ifndef __ASSEMBLER__
>>  /* Don't declare this as a function---we want it's entry-point, not
>>     it's function descriptor... */
>> -extern int _dl_sysinfo_break attribute_hidden;
>> +/* Use section ".text" to force far GPREL64 relocation instead of
>> +   GPREL22 . */
>> +extern int _dl_sysinfo_break attribute_hidden __attribute__((section(".text")));
> 
> More context:
> 
> | /* Don't declare this as a function---we want it's entry-point, not
> |    it's function descriptor... */
> | extern int _dl_sysinfo_break attribute_hidden;
> | # define DL_SYSINFO_DEFAULT ((uintptr_t) &_dl_sysinfo_break)
> | # define DL_SYSINFO_IMPLEMENTATION              \
> |   asm (".text\n\t"                              \
> |        ".hidden _dl_sysinfo_break\n\t"          \
> |        ".proc _dl_sysinfo_break\n\t"            \
> |        "_dl_sysinfo_break:\n\t"                 \
> |        ".prologue\n\t"                          \
> |        ".altrp b6\n\t"                          \
> |        ".body\n\t"                              \
> |        "break 0x100000;\n\t"                    \
> |        "br.ret.sptk.many b6;\n\t"               \
> |        ".endp _dl_sysinfo_break\n\t"            \
> |        ".previous");
> | #endif
> 
> So this seems actually correct because the symbol is defined in .text.
> (I was wondered why this would make .text writable.)

That was my understanding back then as well, and I tested myself the testcase
Sergei has created [1] and at least with gcc from 6 to 13 built with 
build-many-glibcs.py I don't see any relocation failure.  But at same time
I don't see any relocation failure with current code either, so I am not
sure why this is happening with Gentoo toolchain (maybe a incomplete backport?).

---
$ cat mk.bash
#!/usr/bin/bash

if [ $# -eq 0 ]; then
  echo "usage: mk.bash compiler"
  exit 0;
fi

CC=$1

cat > conftest.c << EOF
#ifdef USE_TEXT
extern int asm_f __attribute__((visibility("hidden"))) __attribute__((section(".text")));
#else
extern int asm_f __attribute__((visibility("hidden")));
#endif

long asm_f_ref;

asm (
".text\n\t" \
   ".hidden asm_f\n\t"
   ".proc asm_f\n\t"
"asm_f:\n\t"
   ".prologue\n\t"
   ".body\n\t"
   "br.ret.sptk.many b0;\n\t"
   ".endp asm_f\n\t"
".previous"
);
EOF

for define in "" "-DUSE_TEST"; do
 for static in "" "-static"; do
  for fpie in "" "-fPIE"; do
   for common in "-fcommon" "-fno-common"; do
    echo -n "define=${define} static=${static} common=${common} fpie=${fpie}: "
    $CC conftest.c -o a -O2 -nostdlib -nostartfiles -e asm_f_ref \
            ${static} ${define} ${fpie} ${common} 2>&1 >/dev/null
    if [ $? -eq 0 ]; then
      echo "OK"
    else
      echo "FAIL"
    fi
   done
  done
 done
done

rm conftest.c
---


[1] https://sourceware.org/pipermail/libc-alpha/2020-May/114493.html