AIX: Export symbols from IBMClang IPA objects

When interprocedural analysis is enabled on the IBMClang family of
compilers (via the `-flto` option) then the resulting object files
contain LLVM IR rather than XCOFF objects[1].

ExportImportList needs to detect LLVM IR objects and use the
`ibm-llvm-nm` tool that ships with the compiler to create the extract
the defined symbols.

Without this change, such objects result in an error message from
`dump` and no symbols being exported from the object file.

[1]: https://www.ibm.com/docs/en/openxl-c-and-cpp-aix/17.1.0?topic=compatibility-link-time-optimization-lto

1 files changed, 34 insertions, 12 deletions

diff --git a/Modules/Platform/AIX/ExportImportList b/Modules/Platform/AIX/ExportImportList
index 891bce7..5e16fcb 100755
--- a/Modules/Platform/AIX/ExportImportList
+++ b/Modules/Platform/AIX/ExportImportList
@@ -5,7 +5,7 @@
 # This script is internal to CMake and meant only to be
 # invoked by CMake-generated build systems on AIX.
 
-usage='usage: ExportImportList -o <out-file> [-l <lib>] [-n] [--] <objects>...'
+usage='usage: ExportImportList -o <out-file> -c <compiler> [-l <lib>] [-n] [--] <objects>...'
 
 die() {
     echo "$@" 1>&2; exit 1
@@ -15,11 +15,13 @@ die() {
 out=''
 lib=''
 no_objects=''
+compiler=''
 while test "$#" != 0; do
     case "$1" in
     -l) shift; lib="$1" ;;
     -o) shift; out="$1" ;;
     -n) no_objects='1' ;;
+    -c) shift; compiler="$1" ;;
     --) shift; break ;;
     -*) die "$usage" ;;
     *)  break ;;
@@ -27,27 +29,47 @@ while test "$#" != 0; do
     shift
 done
 test -n "$out" || die "$usage"
+# We need the compiler executable to resolve where the ibm-llvm-nm executable is
+test -n "$compiler" || die "$usage"
 
 # Build a temporary file that atomically replaces the output later.
 out_tmp="$out.tmp$$"
 trap 'rm -f "$out_tmp"' EXIT INT TERM
 > "$out_tmp"
 
+# If IPA was enabled and a compiler from the IBMClang family is used, then
+# the object files contain LLVM bitcode[0] rather than XCOFF objects and so
+# need to be handled differently.
+#
+# [0]: https://www.ibm.com/docs/en/openxl-c-and-cpp-aix/17.1.0?topic=compatibility-link-time-optimization-lto
+NM="$(dirname "$compiler")/../libexec/ibm-llvm-nm"
+
+function IsBitcode {
+    # N4 = first 4 bytes, -tx = output in hexadecimal, -An = don't display offset
+    # cut: trim off the preceding whitespace where the offset would be
+    # 4243code is the hexadecimal magic number for LLVM bitcode
+    [ "$(od -N4 -tx -An $1 | cut -d ' ' -f 2)" == "4243c0de" ];
+}
+
 # Collect symbols exported from all object files.
 if test -z "$no_objects"; then
     for f in "$@"; do
-        dump -tov -X 32_64 "$f" |
-        awk '
-            BEGIN {
-                V["EXPORTED"]=" export"
-                V["PROTECTED"]=" protected"
-            }
-            /^\[[0-9]+\]\tm +[^ ]+ +\.(text|data|bss) +[^ ]+ +(extern|weak) +(EXPORTED|PROTECTED| ) / {
-                if (!match($NF,/^(\.|__sinit|__sterm|__[0-9]+__)/)) {
-                    print $NF V[$(NF-1)]
+        if IsBitcode "$f"; then
+            "$NM" "$f" --defined-only --extern-only --just-symbol-name 2>/dev/null
+        else
+            dump -tov -X 32_64 "$f" |
+            awk '
+                BEGIN {
+                    V["EXPORTED"]=" export"
+                    V["PROTECTED"]=" protected"
+                }
+                /^\[[0-9]+\]\tm +[^ ]+ +\.(text|data|bss) +[^ ]+ +(extern|weak) +(EXPORTED|PROTECTED| ) / {
+                    if (!match($NF,/^(\.|__sinit|__sterm|__[0-9]+__)/)) {
+                        print $NF V[$(NF-1)]
+                    }
                 }
-            }
-        '
+            '
+        fi
     done >> "$out_tmp"
 fi