[llvm] [llvm-profgen] Handle perf mmaps with page sizes larger than 4 KiB (PR #217887)

[Jinjie Huang via llvm-commits]

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@@ -362,25 +362,20 @@ 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.
-  uint64_t PageSize = 0x1000;
   bool SeenFirstLoadableSegment = false;
   for (const typename ELFT::Phdr &Phdr : PhdrRange) {
     if (Phdr.p_type == ELF::PT_INTERP)
       HasInterp = true;
     if (Phdr.p_type == ELF::PT_LOAD) {
       if (!SeenFirstLoadableSegment) {
-        FirstLoadableAddress = Phdr.p_vaddr & ~(PageSize - 1U);
+        // Derive the preferred address corresponding to file offset zero
+        // without assuming a page size.
+        FirstLoadableAddress = Phdr.p_vaddr - Phdr.p_offset;
         SeenFirstLoadableSegment = true;
       }
       if (Phdr.p_flags & ELF::PF_X) {
-        // Segments will always be loaded at a page boundary.
-        PreferredTextSegmentAddresses.push_back(Phdr.p_vaddr &
-                                                ~(PageSize - 1U));
-        TextSegmentOffsets.push_back(Phdr.p_offset & ~(PageSize - 1U));
+        PreferredTextSegmentAddresses.push_back(Phdr.p_vaddr);
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Jinjie-Huang wrote:

`PreferredTextSegmentAddresses` and `TextSegmentOffsets` are no longer stored as 'mmap start addresses'. Instead, they are now stored as the exact segment starts from the ELF. Therefore, we just need to verify that the difference `PreferredTextSegmentAddress - TextSegmentOffset` remains consistent, and there is no need to align them with a specific pagesize.

https://github.com/llvm/llvm-project/pull/217887