Fix unit tests on ppc64

Backport a patch from upstream to fix symbolization on ppc64, and enable
unit tests on that platform.

4 files changed, 122 insertions, 3 deletions

diff --git a/debian/changelog b/debian/changelog
index 6abc1938..9a6cdc08 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -3,6 +3,8 @@ abseil (20230125.3-2) UNRELEASED; urgency=medium
   * Reenable unit tests, which were accidentally disabled in the previous
     version.
   * Backport an upstream patch to allow building tests on mipsel.
+  * Backport a patch from upstream to correct symbolization on ppc64, and
+    enable unit tests on that platform.
 
  -- Benjamin Barenblat <bbaren@debian.org>  Tue, 27 Jun 2023 17:00:12 -0400
 
diff --git a/debian/patches/series b/debian/patches/series
index 66bf33ce..000d6558 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -5,3 +5,4 @@ empty-flags-library.diff
 cordz-info-statistics-test.diff
 pkg-config-directives.diff
 split-hash-tests.diff
+symbolize-ppc64.diff
diff --git a/debian/patches/symbolize-ppc64.diff b/debian/patches/symbolize-ppc64.diff
new file mode 100644
index 00000000..a11c27d4
--- /dev/null
+++ b/debian/patches/symbolize-ppc64.diff
@@ -0,0 +1,118 @@
+From: Benjamin Barenblat <bbaren@google.com>
+Subject: Fix symbolization on PowerPC ELF v1
+Origin: backport, https://github.com/abseil/abseil-cpp/commit/372bfc86105728732fc115af46223d7a4e49f8d9
+
+The big-endian PowerPC ELF ABI (ppc64 in Debian) relies on function descriptors
+mapped in a non-executable segment. Make sure that segment is scanned during
+symbolization. Also correct bounds computation for that segment.
+
+--- a/absl/debugging/symbolize_elf.inc
++++ b/absl/debugging/symbolize_elf.inc
+@@ -648,8 +648,10 @@
+ }
+ 
+ // Return true if an address is inside a section.
+-static bool InSection(const void *address, const ElfW(Shdr) * section) {
+-  const char *start = reinterpret_cast<const char *>(section->sh_addr);
++static bool InSection(const void *address, ptrdiff_t relocation,
++                      const ElfW(Shdr) * section) {
++  const char *start = reinterpret_cast<const char *>(
++      section->sh_addr + static_cast<ElfW(Addr)>(relocation));
+   size_t size = static_cast<size_t>(section->sh_size);
+   return start <= address && address < (start + size);
+ }
+@@ -689,8 +691,8 @@
+   // starting address.  However, we do not always want to use the real
+   // starting address because we sometimes want to symbolize a function
+   // pointer into the .opd section, e.g. FindSymbol(&foo,...).
+-  const bool pc_in_opd =
+-      kPlatformUsesOPDSections && opd != nullptr && InSection(pc, opd);
++  const bool pc_in_opd = kPlatformUsesOPDSections && opd != nullptr &&
++                         InSection(pc, relocation, opd);
+   const bool deref_function_descriptor_pointer =
+       kPlatformUsesOPDSections && opd != nullptr && !pc_in_opd;
+ 
+@@ -730,7 +732,7 @@
+ #endif
+ 
+       if (deref_function_descriptor_pointer &&
+-          InSection(original_start_address, opd)) {
++          InSection(original_start_address, /*relocation=*/0, opd)) {
+         // The opd section is mapped into memory.  Just dereference
+         // start_address to get the first double word, which points to the
+         // function entry.
+@@ -1326,7 +1328,7 @@
+     const int phnum = obj->elf_header.e_phnum;
+     const int phentsize = obj->elf_header.e_phentsize;
+     auto phoff = static_cast<off_t>(obj->elf_header.e_phoff);
+-    size_t num_executable_load_segments = 0;
++    size_t num_interesting_load_segments = 0;
+     for (int j = 0; j < phnum; j++) {
+       ElfW(Phdr) phdr;
+       if (!ReadFromOffsetExact(obj->fd, &phdr, sizeof(phdr), phoff)) {
+@@ -1335,23 +1337,35 @@
+         return false;
+       }
+       phoff += phentsize;
+-      constexpr int rx = PF_X | PF_R;
+-      if (phdr.p_type != PT_LOAD || (phdr.p_flags & rx) != rx) {
+-        // Not a LOAD segment, or not executable code.
++
++#if defined(__powerpc__) && !(_CALL_ELF > 1)
++      // On the PowerPC ELF v1 ABI, function pointers actually point to function
++      // descriptors. These descriptors are stored in an .opd section, which is
++      // mapped read-only. We thus need to look at all readable segments, not
++      // just the executable ones.
++      constexpr int interesting = PF_R;
++#else
++      constexpr int interesting = PF_X | PF_R;
++#endif
++
++      if (phdr.p_type != PT_LOAD
++          || (phdr.p_flags & interesting) != interesting) {
++        // Not a LOAD segment, not executable code, and not a function
++        // descriptor.
+         continue;
+       }
+-      if (num_executable_load_segments < obj->phdr.size()) {
+-        memcpy(&obj->phdr[num_executable_load_segments++], &phdr, sizeof(phdr));
++      if (num_interesting_load_segments < obj->phdr.size()) {
++        memcpy(&obj->phdr[num_interesting_load_segments++], &phdr, sizeof(phdr));
+       } else {
+         ABSL_RAW_LOG(
+-            WARNING, "%s: too many executable LOAD segments: %zu >= %zu",
+-            obj->filename, num_executable_load_segments, obj->phdr.size());
++            WARNING, "%s: too many interesting LOAD segments: %zu >= %zu",
++            obj->filename, num_interesting_load_segments, obj->phdr.size());
+         break;
+       }
+     }
+-    if (num_executable_load_segments == 0) {
+-      // This object has no "r-x" LOAD segments. That's unexpected.
+-      ABSL_RAW_LOG(WARNING, "%s: no executable LOAD segments", obj->filename);
++    if (num_interesting_load_segments == 0) {
++      // This object has no interesting LOAD segments. That's unexpected.
++      ABSL_RAW_LOG(WARNING, "%s: no interesting LOAD segments", obj->filename);
+       return false;
+     }
+   }
+@@ -1379,8 +1393,8 @@
+         // X in the file will have a start address of [true relocation]+X.
+         relocation = static_cast<ptrdiff_t>(start_addr - obj->offset);
+ 
+-        // Note: some binaries have multiple "rx" LOAD segments. We must
+-        // find the right one.
++        // Note: some binaries have multiple LOAD segments that can contain
++        // function pointers. We must find the right one.
+         ElfW(Phdr) *phdr = nullptr;
+         for (size_t j = 0; j < obj->phdr.size(); j++) {
+           ElfW(Phdr) &p = obj->phdr[j];
+@@ -1390,7 +1404,7 @@
+             ABSL_RAW_CHECK(p.p_type == PT_NULL, "unexpected p_type");
+             break;
+           }
+-          if (pc < reinterpret_cast<void *>(start_addr + p.p_memsz)) {
++          if (pc < reinterpret_cast<void *>(start_addr + p.p_vaddr + p.p_memsz)) {
+             phdr = &p;
+             break;
+           }
diff --git a/debian/rules b/debian/rules
index e835a80d..7f76c033 100755
--- a/debian/rules
+++ b/debian/rules
@@ -19,10 +19,8 @@ export DEB_BUILD_MAINT_OPTIONS = hardening=+bindnow reproducible=+fixfilepath
 
 # Unit tests require more than 2 GB of RAM, so disable them on mipsel.
 #
-# Unit tests are not yet passing on ppc64, so disable them there as well.
-#
 # Disable unit tests unconditionally if nocheck is set.
-ifneq ($(filter $(DEB_HOST_ARCH),mipsel ppc64),)
+ifeq ($(DEB_HOST_ARCH),mipsel)
 ABSL_RUN_TESTS=OFF
 else ifneq ($(filter nocheck,$(DEB_BUILD_OPTIONS)),)
 ABSL_RUN_TESTS=OFF