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[Coverage] Darwin: Move __llvm_covmap from __DATA to __LLVM_COV 

Programs with very large __llvm_covmap sections may fail to link on
Darwin because because of out-of-range 32-bit RIP relative references.
It isn't possible to work around this by using the large code model
because it isn't supported on Darwin. One solution is to move the
__llvm_covmap section past the end of the __DATA segment.

=== Testing ===

In addition to check-{llvm,clang,profile}, I performed a link test on a
simple object after injecting ~4GB of padding into __llvm_covmap:

  @__llvm_coverage_padding = internal constant [4000000000 x i8] zeroinitializer, section "__LLVM_COV,__llvm_covmap", align 8

(This test is too expensive to check-in.)

=== Backwards Compatibility ===

This patch should not pose any backwards-compatibility concerns. LLVM
is expected to scan all of the sections in a binary for __llvm_covmap,
so changing its segment shouldn't affect anything. I double-checked this
by loading coverage produced by an unpatched compiler with a patched
llvm-cov.

Suggested by Nick Kledzik.

llvm-svn: 285360
This commit is contained in:
Vedant Kumar 2016-10-27 23:17:51 +00:00
parent b133fbb9a4
commit 75f1de0c1a
2 changed files with 5 additions and 3 deletions
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2
llvm/include/llvm/ProfileData/InstrProf.h
View File

@ -82,7 +82,7 @@ inline StringRef getInstrProfValueProfFuncName() {
/// Return the name of the section containing function coverage mapping
/// data.
inline StringRef getInstrProfCoverageSectionName(bool AddSegment) {
return AddSegment ? "__DATA," INSTR_PROF_COVMAP_SECT_NAME_STR
return AddSegment ? "__LLVM_COV," INSTR_PROF_COVMAP_SECT_NAME_STR
: INSTR_PROF_COVMAP_SECT_NAME_STR;
}

6
llvm/test/Instrumentation/AddressSanitizer/do-not-instrument-globals-darwin.ll
View File

@ -10,12 +10,14 @@ target triple = "x86_64-apple-macosx10.10.0"
; CHECK: @foo_noinst = private global [19 x i8] c"scannerWithString:\00", section "__TEXT,__objc_methname,cstring_literals"
@.str_noinst = private unnamed_addr constant [4 x i8] c"aaa\00", section "llvm.metadata"
@.str_noinst_prof = private unnamed_addr constant [4 x i8] c"aaa\00", section "__DATA,__llvm_covmap"
@.str_noinst_old_cov = private unnamed_addr constant [4 x i8] c"aaa\00", section "__DATA,__llvm_covmap"
@.str_noinst_new_cov = private unnamed_addr constant [4 x i8] c"aaa\00", section "__LLVM_COV,__llvm_covmap"
@.str_noinst_LLVM = private unnamed_addr constant [4 x i8] c"aaa\00", section "__LLVM,__not_visible"
@.str_inst = private unnamed_addr constant [4 x i8] c"aaa\00"
; CHECK-NOT: {{asan_gen.*str_noinst}}
; CHECK-NOT: {{asan_gen.*str_noinst_prof}}
; CHECK-NOT: {{asan_gen.*str_noinst_old_cov}}
; CHECK-NOT: {{asan_gen.*str_noinst_new_cov}}
; CHECK-NOT: {{asan_gen.*str_noinst_LLVM}}
; CHECK: {{asan_gen.*str_inst}}
; CHECK: @asan.module_ctor