Re: [PATCH] Revert "Correctly determine libc.so 'OUTPUT_FORMAT' when cross-compiling."

[Palmer Dabbelt <palmer@rivosinc.com>]

On Tue, 22 Nov 2022 18:59:32 PST (-0800), Vineet Gupta wrote:
> This reverts commit 361d6454c034a920f2c96517c277990d390b9652.
>
> This trips up riscv gnu toolchain builds [1]
>
> riscv ld segfaults when linking libgcc because libc.so linker script
> contains `OUTPUT_FORMAT(elf32-little)` vs. `OUTPUT_FORMAT(elf32-littleriscv)`.

Sounds like a linker bug?

> This patch causes builds to lookup riscv32* prefixed objdump and failing
> to find it falls back to host objdump which is the root of the issue.
> The host objdump in turn generates `OUTPUT_FORMAT(elf32-little)`
>
> riscv glibc multilib builds lack riscv32 prefix binaries. They have a
> single set of "riscv64" prefixed binaries supporting both 32 and 64-bit
> abis: ilp32/ilp32d/lp64/lp64d using -march/-mabi.

Though we _could_ have riscv32-* and riscv64-* binaries (and also 
riscv*- too), it just doesn't make much of a difference as the riscv64-* 
binaries can target everything.  If the answer here is just "fix 
riscv-gnu-toolchain" that seems reasonable to me, but also happy to 
avoid touching that so

Acked-by: Palmer Dabbelt <palmer@rivosinc.com>

Though some sort of global reviewer should take a look here, I 
definately don't understand the glibc build process well enough to 
review this one.

Thanks!

> FWIW I'm not sure how this patch fixed a real problem to begin with.
> At least for the riscv toolchain builds the non-prefixed objdump was
> still from the cross-tools and behaved exactly same as the prefixed one.
> At least it was not picking up the host version which would fail -
> ironically what this patch ended up triggering for riscv.
>
> | $ find TC_INSTALL -name *objdump -exec md5sum {} \;
> | 5fd0b967d4977a4f8bc3a7b7a9318b1d  ./bin/riscv64-unknown-linux-gnu-objdump
> | 5fd0b967d4977a4f8bc3a7b7a9318b1d  ./riscv64-unknown-linux-gnu/bin/objdump
> |
> | $ ./bin/riscv64-unknown-linux-gnu-objdump -f ./xx.lds.so  | grep "file format"
> | ./xx.lds.so:     file format elf32-littleriscv
> |
> | $ ./riscv64-unknown-linux-gnu/bin/objdump -f ./xx.lds.so  | grep "file format"
> | ./xx.lds.so:     file format elf32-littleriscv
>
> [1] https://github.com/riscv-collab/riscv-gnu-toolchain/issues/1161
>
> Signed-off-by: Vineet Gupta <vineetg@rivosinc.com>
> ---
>  aclocal.m4   |  2 ++
>  configure    | 96 ++--------------------------------------------------
>  configure.ac |  1 -
>  3 files changed, 5 insertions(+), 94 deletions(-)
>
> diff --git a/aclocal.m4 b/aclocal.m4
> index 531b11cb6988..3b4df4a37197 100644
> --- a/aclocal.m4
> +++ b/aclocal.m4
> @@ -122,6 +122,8 @@ AS=`$CC -print-prog-name=as`
>  LD=`$CC -print-prog-name=$LDNAME`
>  AR=`$CC -print-prog-name=ar`
>  AC_SUBST(AR)
> +OBJDUMP=`$CC -print-prog-name=objdump`
> +AC_SUBST(OBJDUMP)
>  OBJCOPY=`$CC -print-prog-name=objcopy`
>  AC_SUBST(OBJCOPY)
>  GPROF=`$CC -print-prog-name=gprof`
> diff --git a/configure b/configure
> index cb0996d59e21..fbaa20e040b5 100755
> --- a/configure
> +++ b/configure
> @@ -649,6 +649,7 @@ LD
>  AS
>  GPROF
>  OBJCOPY
> +OBJDUMP
>  AR
>  LN_S
>  INSTALL_DATA
> @@ -684,7 +685,6 @@ sysheaders
>  ac_ct_CXX
>  CXXFLAGS
>  CXX
> -OBJDUMP
>  READELF
>  CPP
>  cross_compiling
> @@ -2963,98 +2963,6 @@ else
>    READELF="$ac_cv_prog_READELF"
>  fi
>
> -if test -n "$ac_tool_prefix"; then
> -  # Extract the first word of "${ac_tool_prefix}objdump", so it can be a program name with args.
> -set dummy ${ac_tool_prefix}objdump; ac_word=$2
> -{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
> -$as_echo_n "checking for $ac_word... " >&6; }
> -if ${ac_cv_prog_OBJDUMP+:} false; then :
> -  $as_echo_n "(cached) " >&6
> -else
> -  if test -n "$OBJDUMP"; then
> -  ac_cv_prog_OBJDUMP="$OBJDUMP" # Let the user override the test.
> -else
> -as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
> -for as_dir in $PATH
> -do
> -  IFS=$as_save_IFS
> -  test -z "$as_dir" && as_dir=.
> -    for ac_exec_ext in '' $ac_executable_extensions; do
> -  if as_fn_executable_p "$as_dir/$ac_word$ac_exec_ext"; then
> -    ac_cv_prog_OBJDUMP="${ac_tool_prefix}objdump"
> -    $as_echo "$as_me:${as_lineno-$LINENO}: found $as_dir/$ac_word$ac_exec_ext" >&5
> -    break 2
> -  fi
> -done
> -  done
> -IFS=$as_save_IFS
> -
> -fi
> -fi
> -OBJDUMP=$ac_cv_prog_OBJDUMP
> -if test -n "$OBJDUMP"; then
> -  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $OBJDUMP" >&5
> -$as_echo "$OBJDUMP" >&6; }
> -else
> -  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
> -$as_echo "no" >&6; }
> -fi
> -
> -
> -fi
> -if test -z "$ac_cv_prog_OBJDUMP"; then
> -  ac_ct_OBJDUMP=$OBJDUMP
> -  # Extract the first word of "objdump", so it can be a program name with args.
> -set dummy objdump; ac_word=$2
> -{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
> -$as_echo_n "checking for $ac_word... " >&6; }
> -if ${ac_cv_prog_ac_ct_OBJDUMP+:} false; then :
> -  $as_echo_n "(cached) " >&6
> -else
> -  if test -n "$ac_ct_OBJDUMP"; then
> -  ac_cv_prog_ac_ct_OBJDUMP="$ac_ct_OBJDUMP" # Let the user override the test.
> -else
> -as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
> -for as_dir in $PATH
> -do
> -  IFS=$as_save_IFS
> -  test -z "$as_dir" && as_dir=.
> -    for ac_exec_ext in '' $ac_executable_extensions; do
> -  if as_fn_executable_p "$as_dir/$ac_word$ac_exec_ext"; then
> -    ac_cv_prog_ac_ct_OBJDUMP="objdump"
> -    $as_echo "$as_me:${as_lineno-$LINENO}: found $as_dir/$ac_word$ac_exec_ext" >&5
> -    break 2
> -  fi
> -done
> -  done
> -IFS=$as_save_IFS
> -
> -fi
> -fi
> -ac_ct_OBJDUMP=$ac_cv_prog_ac_ct_OBJDUMP
> -if test -n "$ac_ct_OBJDUMP"; then
> -  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_ct_OBJDUMP" >&5
> -$as_echo "$ac_ct_OBJDUMP" >&6; }
> -else
> -  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
> -$as_echo "no" >&6; }
> -fi
> -
> -  if test "x$ac_ct_OBJDUMP" = x; then
> -    OBJDUMP="false"
> -  else
> -    case $cross_compiling:$ac_tool_warned in
> -yes:)
> -{ $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: using cross tools not prefixed with host triplet" >&5
> -$as_echo "$as_me: WARNING: using cross tools not prefixed with host triplet" >&2;}
> -ac_tool_warned=yes ;;
> -esac
> -    OBJDUMP=$ac_ct_OBJDUMP
> -  fi
> -else
> -  OBJDUMP="$ac_cv_prog_OBJDUMP"
> -fi
> -
>
>  # We need the C++ compiler only for testing.
>  ac_ext=cpp
> @@ -4672,6 +4580,8 @@ AS=`$CC -print-prog-name=as`
>  LD=`$CC -print-prog-name=$LDNAME`
>  AR=`$CC -print-prog-name=ar`
>
> +OBJDUMP=`$CC -print-prog-name=objdump`
> +
>  OBJCOPY=`$CC -print-prog-name=objcopy`
>
>  GPROF=`$CC -print-prog-name=gprof`
> diff --git a/configure.ac b/configure.ac
> index 20b5e8043fad..0ca4bf56ef76 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -52,7 +52,6 @@ fi
>  AC_SUBST(cross_compiling)
>  AC_PROG_CPP
>  AC_CHECK_TOOL(READELF, readelf, false)
> -AC_CHECK_TOOL(OBJDUMP, objdump, false)
>
>  # We need the C++ compiler only for testing.
>  AC_PROG_CXX