[llvm-profgen] Skip disassembling for PLT section

[wlei]

Summary

Skip disassembling .plt section, then .plt section code will be treated as external code.

[wlei]

Updating D115699: [llvm-profgen] Skip disassembling for PLT section

[wenlei]

llvm/test/tools/llvm-profgen/inline-noprobe2.test

76

are these test changes expected?

[wlei]

llvm/test/tools/llvm-profgen/inline-noprobe2.test

11–12

This will be fixed by https://reviews.llvm.org/D115550

76

Oh, sorry, it's the same to https://reviews.llvm.org/D115538, previously I removed by mistake. Let me removed this here.

[wlei]

remove unrelated test case

[wenlei]

llvm/test/tools/llvm-profgen/inline-noprobe2.test

76

If you put them in a stack, these earlier/unrelated changes won't show up.

But still.. why are the remaining test changes, are they all due to PLT?

[hoy]

llvm/test/tools/llvm-profgen/inline-noprobe2.test

76

Good question. Do the counters changed refer to PLT calls?

llvm/tools/llvm-profgen/ProfiledBinary.cpp

557

Move this above the ShowDisassemblyOnly check?

[wlei]

llvm/test/tools/llvm-profgen/inline-noprobe2.test

76

This patch is in the bottom of the patch stack. It appeared that those counter changes are all fixed by the following two patches. I guess it's due to the wrong leading external addr processing. let me confirm what's wrong.

[wlei]

llvm/test/tools/llvm-profgen/inline-noprobe2.test

76

OK, it turned out that the PLT address is just the leading LBR's target, remembering before the two external fix, the whole samples will be ignored.

0x400540 is plt
400870 0x400870/0x400540/P/-/-/1  0x4008bf/0x400870/P/-/-/7  0x7f7448e88cc1/0x400875/P/-/-/1

llvm/tools/llvm-profgen/ProfiledBinary.cpp

557

objdump also print out ".plt" section, I was thinking to print a section name as a hint we have the ".plt" section there(the size is not empty, we just doesn't disassembly it's body). Otherwise people might misunderstand there is no ".plt" section

[hoy]

llvm/test/tools/llvm-profgen/inline-noprobe2.test

76

I see. So the counters 5.1, 5.3 ... correspond to a call to the PLT entries right?

llvm/tools/llvm-profgen/ProfiledBinary.cpp

557

Makes sense, though I was thinking we'll probably use objdump to look at real disasm, and use llvm-profgen to dump only functions of interest.

[wlei]

llvm/test/tools/llvm-profgen/inline-noprobe2.test

76

Nearby the call to PLT, the code after return from PLT.

range [0x400875, 0x4008bf]

400870:	e8 cb fc ff ff       	callq  400540 <rand@plt>
400875:	48 98                	cltq   
400877:	48 69 c8 1f 85 eb 51 	imul   $0x51eb851f,%rax,%rcx
40087e:	48 89 ca             	mov    %rcx,%rdx
400881:	48 c1 ea 3f          	shr    $0x3f,%rdx
400885:	48 c1 f9 26          	sar    $0x26,%rcx
400889:	01 d1                	add    %edx,%ecx
40088b:	69 c9 c8 00 00 00    	imul   $0xc8,%ecx,%ecx
400891:	29 c8                	sub    %ecx,%eax
400893:	89 04 ab             	mov    %eax,(%rbx,%rbp,4)
400896:	48 83 c5 01          	add    $0x1,%rbp
40089a:	48 81 fd c8 00 00 00 	cmp    $0xc8,%rbp
4008a1:	0f 84 69 ff ff ff    	je     400810 <main+0x30>
4008a7:	40 0f b6 c5          	movzbl %bpl,%eax
4008ab:	69 c0 cd 00 00 00    	imul   $0xcd,%eax,%eax
4008b1:	c1 e8 0a             	shr    $0xa,%eax
4008b4:	83 e0 fe             	and    $0xfffffffe,%eax
4008b7:	8d 04 80             	lea    (%rax,%rax,4),%eax
4008ba:	f7 d8                	neg    %eax
4008bc:	40 00 e8             	add    %bpl,%al
4008bf:	75 af                	jne    400870 <main+0x90>

[hoy]

llvm/test/tools/llvm-profgen/inline-noprobe2.test

76

This is probably unimportant but I'm wondering why the counters don't come with a call target like

;CHECK: 5.1: rand@plt : 10

[wlei]

llvm/test/tools/llvm-profgen/inline-noprobe2.test

76

Oh, because we rand@plt is not a function, remembering we set isFunctionEntry when dwarf name match symbol name, here it doesn't match.

[hoy]

LGTM.

llvm/test/tools/llvm-profgen/inline-noprobe2.test

76

Gotcha, thanks for explanation.

[wenlei]

lgtm, thanks.

llvm/test/tools/llvm-profgen/inline-noprobe2.test

 ; RUN: llvm-profgen --format=text --perfscript=%S/Inputs/artificial-branch.perfscript --binary=%S/Inputs/inline-noprobe2.perfbin --output=%t  --skip-symbolization --use-offset=0
 ; RUN: FileCheck %s --input-file %t --check-prefix=CHECK-ARTIFICIAL-BRANCH
 ; RUN: llvm-profgen --format=text --perfscript=%S/Inputs/inline-noprobe2.perfscript --binary=%S/Inputs/inline-noprobe2.perfbin --output=%t  --skip-symbolization --use-offset=0
 ; RUN: FileCheck %s --input-file %t --check-prefix=CHECK-RAW-PROFILE
 ; RUN: llvm-profgen --format=text --unsymbolized-profile=%t --binary=%S/Inputs/inline-noprobe2.perfbin --output=%t1 --use-offset=0
 ; RUN: FileCheck %s --input-file %t1 --check-prefix=CHECK
 
 ; RUN: llvm-profgen --format=extbinary --perfscript=%S/Inputs/inline-noprobe2.perfscript --binary=%S/Inputs/inline-noprobe2.perfbin --output=%t --populate-profile-symbol-list=1
 ; RUN: llvm-profdata show -show-prof-sym-list -sample %t | FileCheck %s --check-prefix=CHECK-SYM-LIST
 
-; CHECK-ARTIFICIAL-BRANCH: 3
-; CHECK-ARTIFICIAL-BRANCH: 400540-400540:1
-; CHECK-ARTIFICIAL-BRANCH: 400870-400870:2
-; CHECK-ARTIFICIAL-BRANCH: 400875-4008bf:1
-; CHECK-ARTIFICIAL-BRANCH: 2
-; CHECK-ARTIFICIAL-BRANCH: 400870->400540:2
-; CHECK-ARTIFICIAL-BRANCH: 4008bf->400870:2
+; CHECK-ARTIFICIAL-BRANCH: 0
+; CHECK-ARTIFICIAL-BRANCH: 0
 
 ; CHECK-SYM-LIST: Dump profile symbol list
 ; CHECK-SYM-LIST: main
 ; CHECK-SYM-LIST: partition_pivot_first
 ; CHECK-SYM-LIST: partition_pivot_last
 ; CHECK-SYM-LIST: quick_sort
 ; CHECK-SYM-LIST: swap
 

 
 ;CHECK:   1: 18
 ;CHECK:   2: 18
 ;CHECK:   3: 18
 ;CHECK:  6: swap:85
 ;CHECK:   1: 5
 ;CHECK:   2: 5
 ;CHECK:   3: 5
-;CHECK: main:820:0
+;CHECK: main:486:0
 ;CHECK:  0: 0
 ;CHECK:  3: 0
 ;CHECK:  4.1: 0
 ;CHECK:  4.3: 0
-;CHECK:  5.1: 10
-;CHECK:  5.3: 10
-;CHECK:  6: 10
-;CHECK:  6.1: 12
-;CHECK:  6.3: 10
+;CHECK:  5.1: 6
+;CHECK:  5.3: 6
+;CHECK:  6: 6
+;CHECK:  6.1: 6
+;CHECK:  6.3: 6
 ;CHECK:  7: 0
 ;CHECK:  8: 0 quick_sort:1
 ;CHECK:  9: 0
 ;CHECK:  11: 0
 ;CHECK:  14: 0
 ;CHECK:  65499: 0
 
 

llvm/tools/llvm-profgen/ProfiledBinary.cpp

for (section_iterator SI = Obj->section_begin(), SE = Obj->section_end();
     uint64_t SectionOffset = Section.getAddress() - ImageLoadAddr;
     uint64_t SectSize = Section.getSize();
     if (!SectSize)
       continue;
 
     // Register the text section.
     TextSections.insert({SectionOffset, SectSize});
 
-    if (ShowDisassemblyOnly) {
-      StringRef SectionName = unwrapOrError(Section.getName(), FileName);
+
+    if (ShowDisassemblyOnly) {
       outs() << "\nDisassembly of section " << SectionName;
       outs() << " [" << format("0x%" PRIx64, Section.getAddress()) << ", "
              << format("0x%" PRIx64, Section.getAddress() + SectSize)
              << "]:\n\n";
     }
 
+    if (SectionName == ".plt")
+      continue;
+
     // Get the section data.
     ArrayRef<uint8_t> Bytes =
         arrayRefFromStringRef(unwrapOrError(Section.getContents(), FileName));
 
     // Get the list of all the symbols in this section.
     SectionSymbolsTy &Symbols = AllSymbols[Section];
 
     // Disassemble symbol by symbol.