[llvm] r370072 - [JITLink] Don't under-align zero-fill sections.

[Lang Hames via llvm-commits]

Author: lhames
Date: Tue Aug 27 08:22:23 2019
New Revision: 370072

URL: http://llvm.org/viewvc/llvm-project?rev=370072&view=rev
Log:
[JITLink] Don't under-align zero-fill sections.

If content sections have lower alignment than zero-fill sections then bump the
overall segment alignment to avoid under-aligning the zero-fill sections.

Added:
    llvm/trunk/test/ExecutionEngine/JITLink/X86/MachO_zero_fill_alignment.s
Modified:
    llvm/trunk/lib/ExecutionEngine/JITLink/JITLinkGeneric.cpp

Modified: llvm/trunk/lib/ExecutionEngine/JITLink/JITLinkGeneric.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/ExecutionEngine/JITLink/JITLinkGeneric.cpp?rev=370072&r1=370071&r2=370072&view=diff
==============================================================================
--- llvm/trunk/lib/ExecutionEngine/JITLink/JITLinkGeneric.cpp (original)
+++ llvm/trunk/lib/ExecutionEngine/JITLink/JITLinkGeneric.cpp Tue Aug 27 08:22:23 2019
@@ -238,60 +238,47 @@ Error JITLinkerBase::allocateSegments(co
 
     // Calculate segment content size.
     size_t SegContentSize = 0;
+    uint32_t SegContentAlign = 1;
     for (auto &SI : SegLayout.ContentSections) {
       assert(!SI.S->atoms_empty() && "Sections in layout must not be empty");
       assert(!SI.Atoms.empty() && "Section layouts must not be empty");
 
       // Bump to section alignment before processing atoms.
       SegContentSize = alignTo(SegContentSize, SI.S->getAlignment());
+      SegContentAlign = std::max(SegContentAlign, SI.S->getAlignment());
 
       for (auto *DA : SI.Atoms) {
         SegContentSize = alignTo(SegContentSize, DA->getAlignment());
         SegContentSize += DA->getSize();
+        SegContentAlign = std::max(SegContentAlign, DA->getAlignment());
       }
     }
 
-    // Get segment content alignment.
-    unsigned SegContentAlign = 1;
-    if (!SegLayout.ContentSections.empty()) {
-      auto &FirstContentSection = SegLayout.ContentSections.front();
-      SegContentAlign =
-          std::max(FirstContentSection.S->getAlignment(),
-                   FirstContentSection.Atoms.front()->getAlignment());
-    }
-
     // Calculate segment zero-fill size.
     uint64_t SegZeroFillSize = 0;
+    uint32_t SegZeroFillAlign = 1;
+
     for (auto &SI : SegLayout.ZeroFillSections) {
       assert(!SI.S->atoms_empty() && "Sections in layout must not be empty");
       assert(!SI.Atoms.empty() && "Section layouts must not be empty");
 
       // Bump to section alignment before processing atoms.
       SegZeroFillSize = alignTo(SegZeroFillSize, SI.S->getAlignment());
+      SegZeroFillAlign = std::max(SegZeroFillAlign, SI.S->getAlignment());
 
       for (auto *DA : SI.Atoms) {
         SegZeroFillSize = alignTo(SegZeroFillSize, DA->getAlignment());
         SegZeroFillSize += DA->getSize();
+        SegZeroFillAlign = std::max(SegZeroFillAlign, SI.S->getAlignment());
       }
     }
 
-    // Calculate segment zero-fill alignment.
-    uint32_t SegZeroFillAlign = 1;
-
-    if (!SegLayout.ZeroFillSections.empty()) {
-      auto &FirstZeroFillSection = SegLayout.ZeroFillSections.front();
-      SegZeroFillAlign =
-          std::max(FirstZeroFillSection.S->getAlignment(),
-                   FirstZeroFillSection.Atoms.front()->getAlignment());
-    }
-
-    if (SegContentSize == 0)
-      SegContentAlign = SegZeroFillAlign;
-
-    if (SegContentAlign % SegZeroFillAlign != 0)
-      return make_error<JITLinkError>("First content atom alignment does not "
-                                      "accommodate first zero-fill atom "
-                                      "alignment");
+    assert(isPowerOf2_32(SegContentAlign) &&
+           "Expected content alignment to be power of 2");
+    assert(isPowerOf2_32(SegZeroFillAlign) &&
+           "Expected zero-fill alignment to be power of 2");
+    // Round content alignment up to segment alignment.
+    SegContentAlign = std::max(SegContentAlign, SegZeroFillAlign);
 
     Segments[Prot] = {SegContentSize, SegContentAlign, SegZeroFillSize,
                       SegZeroFillAlign};

Added: llvm/trunk/test/ExecutionEngine/JITLink/X86/MachO_zero_fill_alignment.s
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/ExecutionEngine/JITLink/X86/MachO_zero_fill_alignment.s?rev=370072&view=auto
==============================================================================
--- llvm/trunk/test/ExecutionEngine/JITLink/X86/MachO_zero_fill_alignment.s (added)
+++ llvm/trunk/test/ExecutionEngine/JITLink/X86/MachO_zero_fill_alignment.s Tue Aug 27 08:22:23 2019
@@ -0,0 +1,14 @@
+# RUN: rm -rf %t && mkdir -p %t
+# RUN: llvm-mc -triple=x86_64-apple-macosx10.9 -filetype=obj -o %t/macho_zero_fill_align.o %s
+# RUN: llvm-jitlink -noexec %t/macho_zero_fill_align.o -entry higher_zero_fill_align
+
+        .section        __DATA,__data
+        .globl low_aligned_data
+        .p2align  0
+low_aligned_data:
+        .byte 42
+
+        .globl higher_zero_fill_align
+.zerofill __DATA,__zero_fill,higher_zero_fill_align,8,3
+
+.subsections_via_symbols