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llvm-project/lld/test/ELF/relocation-copy-alias.s

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ELF: Create dynamic symbols for symbol aliases of copy relocations. For each copy relocation that we create, look through the DSO's symbol table for aliases and create a dynamic symbol for each one. This causes the copy relocation to correctly interpose any aliases. Copy relocations are relatively uncommon (on my machine, 56% of binaries in /usr/bin have no copy relocations probably due to being PIEs, 97% of them have <10, and the binary with the largest number of them has 97) so it's probably fine to do this in a relatively inefficient way. Differential Revision: http://reviews.llvm.org/D18731 llvm-svn: 265354
2016-04-05 06:29:24 +08:00
// REQUIRES: x86
// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %p/Inputs/relocation-copy-alias.s -o %t2.o
// RUN: ld.lld -shared %t2.o -o %t.so
// RUN: ld.lld %t.o %t.so -o %t3
// RUN: llvm-readobj --dyn-symbols -r --expand-relocs %t3 | FileCheck %s
.global _start
_start:
movl $5, a1
movl $5, b1
movl $5, b2
// CHECK: .rela.dyn {
// CHECK-NEXT: Relocation {
// CHECK-NEXT: Offset:
// CHECK-NEXT: Type: R_X86_64_COPY
// CHECK-NEXT: Symbol: a1
// CHECK-NEXT: Addend: 0x0
// CHECK-NEXT: }
// CHECK-NEXT: Relocation {
// CHECK-NEXT: Offset:
// CHECK-NEXT: Type: R_X86_64_COPY
// CHECK-NEXT: Symbol: b1
// CHECK-NEXT: Addend: 0x0
// CHECK-NEXT: }
// CHECK-NEXT: }
// CHECK: Name: a1
// CHECK-NEXT: Value: [[A:.*]]
// CHECK-NEXT: Size: 1
// CHECK-NEXT: Binding: Global (0x1)
// CHECK-NEXT: Type: Object (0x1)
// CHECK-NEXT: Other: 0
// CHECK-NEXT: Section: .bss (0x7)
// CHECK: Name: b1
// CHECK-NEXT: Value: [[B:.*]]
// CHECK-NEXT: Size: 1
Store the binding in the Symbol. This remove a fixme, cleans up the weak undef interaction with archives and lets us keep weak undefs still weak if they resolve to shared. llvm-svn: 267555
2016-04-26 21:50:46 +08:00
// CHECK-NEXT: Binding: Global
ELF: Create dynamic symbols for symbol aliases of copy relocations. For each copy relocation that we create, look through the DSO's symbol table for aliases and create a dynamic symbol for each one. This causes the copy relocation to correctly interpose any aliases. Copy relocations are relatively uncommon (on my machine, 56% of binaries in /usr/bin have no copy relocations probably due to being PIEs, 97% of them have <10, and the binary with the largest number of them has 97) so it's probably fine to do this in a relatively inefficient way. Differential Revision: http://reviews.llvm.org/D18731 llvm-svn: 265354
2016-04-05 06:29:24 +08:00
// CHECK-NEXT: Type: Object (0x1)
// CHECK-NEXT: Other: 0
// CHECK-NEXT: Section: .bss
// CHECK: Name: b2
// CHECK-NEXT: Value: [[B]]
// CHECK-NEXT: Size: 1
Store the binding in the Symbol. This remove a fixme, cleans up the weak undef interaction with archives and lets us keep weak undefs still weak if they resolve to shared. llvm-svn: 267555
2016-04-26 21:50:46 +08:00
// CHECK-NEXT: Binding: Global
ELF: Create dynamic symbols for symbol aliases of copy relocations. For each copy relocation that we create, look through the DSO's symbol table for aliases and create a dynamic symbol for each one. This causes the copy relocation to correctly interpose any aliases. Copy relocations are relatively uncommon (on my machine, 56% of binaries in /usr/bin have no copy relocations probably due to being PIEs, 97% of them have <10, and the binary with the largest number of them has 97) so it's probably fine to do this in a relatively inefficient way. Differential Revision: http://reviews.llvm.org/D18731 llvm-svn: 265354
2016-04-05 06:29:24 +08:00
// CHECK-NEXT: Type: Object (0x1)
// CHECK-NEXT: Other: 0
// CHECK-NEXT: Section: .bss
// CHECK: Name: a2
// CHECK-NEXT: Value: [[A]]
// CHECK-NEXT: Size: 1
ELF: New symbol table design. This patch implements a new design for the symbol table that stores SymbolBodies within a memory region of the Symbol object. Symbols are mutated by constructing SymbolBodies in place over existing SymbolBodies, rather than by mutating pointers. As mentioned in the initial proposal [1], this memory layout helps reduce the cache miss rate by improving memory locality. Performance numbers: old(s) new(s) Without debug info: chrome 7.178 6.432 (-11.5%) LLVMgold.so 0.505 0.502 (-0.5%) clang 0.954 0.827 (-15.4%) llvm-as 0.052 0.045 (-15.5%) With debug info: scylla 5.695 5.613 (-1.5%) clang 14.396 14.143 (-1.8%) Performance counter results show that the fewer required indirections is indeed the cause of the improved performance. For example, when linking chrome, stalled cycles decreases from 14,556,444,002 to 12,959,238,310, and instructions per cycle increases from 0.78 to 0.83. We are also executing many fewer instructions (15,516,401,933 down to 15,002,434,310), probably because we spend less time allocating SymbolBodies. The new mechanism by which symbols are added to the symbol table is by calling add* functions on the SymbolTable. In this patch, I handle local symbols by storing them inside "unparented" SymbolBodies. This is suboptimal, but if we do want to try to avoid allocating these SymbolBodies, we can probably do that separately. I also removed a few members from the SymbolBody class that were only being used to pass information from the input file to the symbol table. This patch implements the new design for the ELF linker only. I intend to prepare a similar patch for the COFF linker. [1] http://lists.llvm.org/pipermail/llvm-dev/2016-April/098832.html Differential Revision: http://reviews.llvm.org/D19752 llvm-svn: 268178
2016-05-01 12:55:03 +08:00
// CHECK-NEXT: Binding: Weak
ELF: Create dynamic symbols for symbol aliases of copy relocations. For each copy relocation that we create, look through the DSO's symbol table for aliases and create a dynamic symbol for each one. This causes the copy relocation to correctly interpose any aliases. Copy relocations are relatively uncommon (on my machine, 56% of binaries in /usr/bin have no copy relocations probably due to being PIEs, 97% of them have <10, and the binary with the largest number of them has 97) so it's probably fine to do this in a relatively inefficient way. Differential Revision: http://reviews.llvm.org/D18731 llvm-svn: 265354
2016-04-05 06:29:24 +08:00
// CHECK-NEXT: Type: Object (0x1)
// CHECK-NEXT: Other: 0
// CHECK-NEXT: Section: .bss
// CHECK: Name: b3
// CHECK-NEXT: Value: [[B]]
// CHECK-NEXT: Size: 1
ELF: New symbol table design. This patch implements a new design for the symbol table that stores SymbolBodies within a memory region of the Symbol object. Symbols are mutated by constructing SymbolBodies in place over existing SymbolBodies, rather than by mutating pointers. As mentioned in the initial proposal [1], this memory layout helps reduce the cache miss rate by improving memory locality. Performance numbers: old(s) new(s) Without debug info: chrome 7.178 6.432 (-11.5%) LLVMgold.so 0.505 0.502 (-0.5%) clang 0.954 0.827 (-15.4%) llvm-as 0.052 0.045 (-15.5%) With debug info: scylla 5.695 5.613 (-1.5%) clang 14.396 14.143 (-1.8%) Performance counter results show that the fewer required indirections is indeed the cause of the improved performance. For example, when linking chrome, stalled cycles decreases from 14,556,444,002 to 12,959,238,310, and instructions per cycle increases from 0.78 to 0.83. We are also executing many fewer instructions (15,516,401,933 down to 15,002,434,310), probably because we spend less time allocating SymbolBodies. The new mechanism by which symbols are added to the symbol table is by calling add* functions on the SymbolTable. In this patch, I handle local symbols by storing them inside "unparented" SymbolBodies. This is suboptimal, but if we do want to try to avoid allocating these SymbolBodies, we can probably do that separately. I also removed a few members from the SymbolBody class that were only being used to pass information from the input file to the symbol table. This patch implements the new design for the ELF linker only. I intend to prepare a similar patch for the COFF linker. [1] http://lists.llvm.org/pipermail/llvm-dev/2016-April/098832.html Differential Revision: http://reviews.llvm.org/D19752 llvm-svn: 268178
2016-05-01 12:55:03 +08:00
// CHECK-NEXT: Binding: Weak
ELF: Create dynamic symbols for symbol aliases of copy relocations. For each copy relocation that we create, look through the DSO's symbol table for aliases and create a dynamic symbol for each one. This causes the copy relocation to correctly interpose any aliases. Copy relocations are relatively uncommon (on my machine, 56% of binaries in /usr/bin have no copy relocations probably due to being PIEs, 97% of them have <10, and the binary with the largest number of them has 97) so it's probably fine to do this in a relatively inefficient way. Differential Revision: http://reviews.llvm.org/D18731 llvm-svn: 265354
2016-04-05 06:29:24 +08:00
// CHECK-NEXT: Type: Object (0x1)
// CHECK-NEXT: Other: 0
// CHECK-NEXT: Section: .bss