[PATCH] D110795: [llvm-profgen] Fix alignment in preferred based calculation

[Wenlei He via Phabricator via llvm-commits]

wenlei created this revision.
wenlei added reviewers: hoy, wlei, wmi.
Herald added subscribers: modimo, lxfind.
wenlei requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

We used the segment alignment in elf header to assume the loader alignment. However this is incorrect because loader alignment is always the same as page size. If segment needs to be aligned at load time, linker will set aligned address as virtual address in elf header.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D110795

Files:
  llvm/tools/llvm-profgen/ProfiledBinary.cpp


Index: llvm/tools/llvm-profgen/ProfiledBinary.cpp
===================================================================
--- llvm/tools/llvm-profgen/ProfiledBinary.cpp
+++ llvm/tools/llvm-profgen/ProfiledBinary.cpp
@@ -233,11 +233,17 @@
 template <class ELFT>
 void ProfiledBinary::setPreferredTextSegmentAddresses(const ELFFile<ELFT> &Obj, StringRef FileName) {
   const auto &PhdrRange = unwrapOrError(Obj.program_headers(), FileName);
+  // FIXME: This should be the page size of the system running profiling.
+  // However such info isn't available at post-processing time, assuming
+  // 4K page now. Note that we don't use EXEC_PAGESIZE from <linux/param.h>
+  // because we may build the tools on non-linux.
+  uint32_t PageSize = 0x1000;
   for (const typename ELFT::Phdr &Phdr : PhdrRange) {
     if ((Phdr.p_type == ELF::PT_LOAD) && (Phdr.p_flags & ELF::PF_X)) {
         // Segments will always be loaded at a page boundary.
-        PreferredTextSegmentAddresses.push_back(Phdr.p_vaddr & ~(Phdr.p_align - 1U));
-        TextSegmentOffsets.push_back(Phdr.p_offset & ~(Phdr.p_align - 1U));
+        PreferredTextSegmentAddresses.push_back(Phdr.p_vaddr &
+                                                ~(PageSize - 1U));
+        TextSegmentOffsets.push_back(Phdr.p_offset & ~(PageSize - 1U));
       }
   }
 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D110795.376081.patch
Type: text/x-patch
Size: 1318 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20210930/7c95e926/attachment.bin>