AIX: Fix support for editing XCOFF binary inside an archive

When AIX stores a `.so` inside a `.a` archive, the loader section is
aligned to maximum of the text and data alignment.  In commit 98013ad1ca
(cmXCOFF: Add support for editing binary inside an archive, 2024-07-01)
we only accounted for the data alignment.

Issue: #26275

1 files changed, 18 insertions, 17 deletions

diff --git a/Source/cmXCOFF.cxx b/Source/cmXCOFF.cxx
index 923b6d9..6fd6fbf 100644
--- a/Source/cmXCOFF.cxx
+++ b/Source/cmXCOFF.cxx
@@ -209,7 +209,10 @@ Impl<XCOFF>::Impl(cmXCOFF* external, std::unique_ptr<std::iostream> fin,
     this->SetErrorMessage("XCOFF loader section missing.");
     return;
   }
-  this->bytes_to_align = this->AuxHeader.o_algndata;
+  this->bytes_to_align =
+    this->AuxHeader.o_algntext > this->AuxHeader.o_algndata
+    ? this->AuxHeader.o_algntext
+    : this->AuxHeader.o_algndata;
   if (!this->Stream->seekg((this->AuxHeader.o_snloader - 1) *
                              sizeof(typename XCOFF::scnhdr),
                            std::ios::cur)) {
@@ -376,16 +379,6 @@ IsArchive check_if_big_archive(const char* fname)
   }
 }
 
-size_t getLastWordLen(const std::string& path)
-{
-  std::size_t lastSlashPos = path.find_last_of("/\\");
-  if (lastSlashPos == std::string::npos) {
-    return path.length();
-  }
-
-  return (path.length() - lastSlashPos - 1);
-}
-
 //============================================================================
 // External class implementation.
 
@@ -429,14 +422,22 @@ cmXCOFF::cmXCOFF(const char* fname, Mode mode)
     ar_hdr arHeader;
     f->read(reinterpret_cast<char*>(&arHeader), sizeof(ar_hdr));
 
-    // We will sometimes get /opt/freeware/lib/libshared.a. So extract
-    // the last part only.
-    // Example: libshared.a [We need to length of "libshared.a" characters].
-    archive_name_length = static_cast<int>(getLastWordLen(std::string(fname)));
+    {
+      errno = 0;
+      char* ar_namlen_endp;
+      unsigned long ar_namlen =
+        strtoul(arHeader.ar_namlen, &ar_namlen_endp, 10);
+      if ((ar_namlen_endp != arHeader.ar_namlen) && (errno == 0)) {
+        archive_name_length = static_cast<int>(ar_namlen);
+      } else {
+        this->ErrorMessage = "Error parsing archive name length.";
+        return;
+      }
+    }
 
-    // Move to the next even byte.
+    // Round off to even byte.
     if (archive_name_length % 2 == 0) {
-      nextEvenByte = archive_name_length + 2;
+      nextEvenByte = archive_name_length;
     } else {
       nextEvenByte = archive_name_length + 1;
     }