Support multithreading

[bjorn3]

Currently atomics are not atomic.

Blocked on https://github.com/CraneStation/cranelift/issues/582

[bjorn3]

This would also require TLS support. (not the protocol, but thread-local storage)

Edit: opened bytecodealliance/cranelift#963

[philipc]

I am interested in adding TLS support to the object crate, and this would make a good test for it. Is this something you would be interested in using?

[bjorn3]

Sure @philipc.

[bjorn3]

https://github.com/bjorn3/rustc_codegen_cranelift/tree/wip_tls contains a test for tls support.

[bjorn3]

#![feature(thread_local)]

#[thread_local]
static mut A: u8 = 42;

pub unsafe fn __get_it() -> *mut u8 {
    &mut A
}

$ rustc --crate-type lib tls.rs -Ccodegen-units=1 -Clto=no -O --emit obj,llvm-ir

; ModuleID = 'tls.3a1fbbbh-cgu.0'
source_filename = "tls.3a1fbbbh-cgu.0"
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.7.0"

@_ZN3tls1A17h13af140b93a46e97E = internal thread_local global <{ [1 x i8] }> <{ [1 x i8] c"*" }>, section "__DATA,__thread_data", align 1

; tls::__get_it
; Function Attrs: norecurse nounwind readnone uwtable
define i8* @_ZN3tls8__get_it17h59d6925afa6bde3cE() unnamed_addr #0 {
start:
  ret i8* getelementptr inbounds (<{ [1 x i8] }>, <{ [1 x i8] }>* @_ZN3tls1A17h13af140b93a46e97E, i64 0, i32 0, i64 0)
}

attributes #0 = { norecurse nounwind readnone uwtable "no-frame-pointer-elim"="true" "probe-stack"="__rust_probestack" "target-cpu"="core2" }

Generated asm, relocations and sections

MacOS

Mach-o OBJECT x86_64-little-endian @ 0x0:

LoadCommands(4):
   0 LC_SEGMENT_64
   1 LC_VERSION_MIN_MACOSX
   2 LC_SYMTAB
   3 LC_DYSYMTAB

Segments(1):
  Segment   # Sections  
            5           
         Idx   Name               Addr    Size    Offset   Align   Reloff   Nrelocs   Flags       
         0     __text             0x0     0xf     0x270    4       0x2f8    1         0x80000400  
         1     __thread_data      0xf     0x1     0x27f    0       0x0      0         0x11        
         2     __thread_vars      0x10    0x18    0x280    0       0x300    2         0x13        
         3     __compact_unwind   0x28    0x20    0x298    3       0x310    1         0x2000000   
         4     __eh_frame         0x48    0x40    0x2b8    3       0x0      0         0x6800000b  


Relocations(4):
  Segment   Section   Count  
  __TEXT    __text    1      
         Type               Offset   Length   PIC     Extern   SymbolNum   Symbol                          
         X86_64_RELOC_TLV   0x7      2        true    true     0x0         __ZN3tls1A17h13af140b93a46e97E  

  Segment   Section         Count  
  __DATA    __thread_vars   2      
         Type                    Offset   Length   PIC      Extern   SymbolNum   Symbol                                   
         X86_64_RELOC_UNSIGNED   0x10     3        false    true     0x1         __ZN3tls1A17h13af140b93a46e97E$tlv$init  
         X86_64_RELOC_UNSIGNED   0x0      3        false    true     0x3         __tlv_bootstrap                          

  Segment   Section            Count  
  __LD      __compact_unwind   1      
         Type                    Offset   Length   PIC      Extern   SymbolNum   Symbol         
         X86_64_RELOC_UNSIGNED   0x0      3        false    false    0x1         __TEXT.__text  


Symbols(4):
  Offset   Name                                      Section                Global   Undefined  
  0x10     __ZN3tls1A17h13af140b93a46e97E            __DATA.__thread_vars   false    false      
  0xf      __ZN3tls1A17h13af140b93a46e97E$tlv$init   __DATA.__thread_data   false    false      
  0x0      __ZN3tls8__get_it17h59d6925afa6bde3cE     __TEXT.__text          true     false      
  0x0      __tlv_bootstrap                           None                   true     true       

Exports(0):

Imports(0):

Libraries(0):

Name: None
is_64: true
is_lib: false
little_endian: true
entry: 0

Disassembly of section __TEXT,__text:
__ZN3tls8__get_it17h59d6925afa6bde3cE:
       0:	55 	pushq	%rbp
       1:	48 89 e5 	movq	%rsp, %rbp
       4:	48 8b 3d 00 00 00 00 	movq	(%rip), %rdi
		0000000000000007:  X86_64_RELOC_TLV	__ZN3tls1A17h13af140b93a46e97E@TLVP
       b:	ff 17 	callq	*(%rdi)
       d:	5d 	popq	%rbp
       e:	c3 	retq
Disassembly of section __DATA,__thread_data:
__ZN3tls1A17h13af140b93a46e97E$tlv$init:
       f:	2a  <unknown>
Disassembly of section __DATA,__thread_vars:
__ZN3tls1A17h13af140b93a46e97E:
      10:	00 00 	addb	%al, (%rax)
		0000000000000010:  X86_64_RELOC_UNSIGNED	__tlv_bootstrap
      12:	00 00 	addb	%al, (%rax)
      14:	00 00 	addb	%al, (%rax)
      16:	00 00 	addb	%al, (%rax)
      18:	00 00 	addb	%al, (%rax)
      1a:	00 00 	addb	%al, (%rax)
      1c:	00 00 	addb	%al, (%rax)
      1e:	00 00 	addb	%al, (%rax)
      20:	00 00 	addb	%al, (%rax)
		0000000000000020:  X86_64_RELOC_UNSIGNED	__ZN3tls1A17h13af140b93a46e97E$tlv$init
      22:	00 00 	addb	%al, (%rax)
      24:	00 00 	addb	%al, (%rax)
      26:	00 00 	addb	%al, (%rax)

Linux

ELF REL X86_64-little-endian @ 0x0:

e_phoff: 0x0 e_shoff: 0x228 e_flags: 0x0 e_ehsize: 64 e_phentsize: 0 e_phnum: 0 e_shentsize: 64 e_shnum: 10 e_shstrndx: 1

ProgramHeaders(0):
  

SectionHeaders(10):
  Idx   Name                                                      Type   Flags              Offset   Addr   Size    Link         Entsize   Align  
  0                                                           SHT_NULL                      0x0      0x0    0x0                  0x0       0x0    
  1     .strtab                                             SHT_STRTAB                      0x178    0x0    0xad                 0x0       0x1    
  2     .text                                             SHT_PROGBITS   ALLOC EXECINSTR    0x40     0x0    0x0                  0x0       0x4    
  3     .text._ZN3tls8__get_it17h59d6925afa6bde3cE        SHT_PROGBITS   ALLOC EXECINSTR    0x40     0x0    0x16                 0x0       0x10   
  4     .rela.text._ZN3tls8__get_it17h59d6925afa6bde3cE       SHT_RELA                      0x118    0x0    0x48    .symtab(9)   0x18      0x8    
  5     .tdata._ZN3tls1A17h13af140b93a46e97E              SHT_PROGBITS   WRITE ALLOC TLS    0x56     0x0    0x1                  0x0       0x1    
  6     .note.GNU-stack                                   SHT_PROGBITS                      0x57     0x0    0x0                  0x0       0x1    
  7     .eh_frame                                          UNKNOWN_SHT   ALLOC              0x58     0x0    0x30                 0x0       0x8    
  8     .rela.eh_frame                                        SHT_RELA                      0x160    0x0    0x18    .symtab(9)   0x18      0x8    
  9     .symtab                                             SHT_SYMTAB                      0x88     0x0    0x90    .strtab(1)   0x18      0x8    

Syms(6):
               Addr   Bind       Type        Symbol                                 Size    Section                                         Other  
                 0    LOCAL      NOTYPE                                             0x0                                                     0x0    
                 0    LOCAL      FILE        tls.3a1fbbbh-cgu.0                     0x0     ABS                                             0x0    
                 0    LOCAL      TLS         _ZN3tls1A17h13af140b93a46e97E          0x1     .tdata._ZN3tls1A17h13af140b93a46e97E(5)         0x0    
                 0    LOCAL      SECTION                                            0x0     .text._ZN3tls8__get_it17h59d6925afa6bde3cE(3)   0x0    
                 0    GLOBAL     FUNC        _ZN3tls8__get_it17h59d6925afa6bde3cE   0x16    .text._ZN3tls8__get_it17h59d6925afa6bde3cE(3)   0x0    
                 0    GLOBAL     NOTYPE      __tls_get_addr                         0x0                                                     0x0    

Dyn Syms(0):
  

Dynamic Relas(0):

Dynamic Rel(0):

Plt Relocations(0):

Shdr Relocations(4):
  .text._ZN3tls8__get_it17h59d6925afa6bde3cE(3)
               4 X86_64_TLSLD _ZN3tls1A17h13af140b93a46e97E+-4
               9 X86_64_PLT32 __tls_get_addr+-4
              10 X86_64_DTPOFF32 _ZN3tls1A17h13af140b93a46e97E

  .eh_frame(1)
              20 X86_64_PC32 .text._ZN3tls8__get_it17h59d6925afa6bde3cE


Dynamic: None


Libraries(0):

Soname: None
Interpreter: None
is_64: true
is_lib: false
little_endian: true
bias: 0x0
entry: 0

Disassembly of section .text._ZN3tls8__get_it17h59d6925afa6bde3cE:
_ZN3tls8__get_it17h59d6925afa6bde3cE:
       0:	50 	pushq	%rax
       1:	48 8d 3d 00 00 00 00 	leaq	(%rip), %rdi
		0000000000000004:  R_X86_64_TLSLD	_ZN3tls1A17h13af140b93a46e97E-4
       8:	e8 00 00 00 00 	callq	0 <_ZN3tls8__get_it17h59d6925afa6bde3cE+0xd>
		0000000000000009:  R_X86_64_PLT32	__tls_get_addr-4
       d:	48 8d 80 00 00 00 00 	leaq	(%rax), %rax
		0000000000000010:  R_X86_64_DTPOFF32	_ZN3tls1A17h13af140b93a46e97E
      14:	59 	popq	%rcx
      15:	c3 	retq
Disassembly of section .rela.text._ZN3tls8__get_it17h59d6925afa6bde3cE:
.rela.text._ZN3tls8__get_it17h59d6925afa6bde3cE:
       0:	04 00 	addb	$0, %al
       2:	00 00 	addb	%al, (%rax)
       4:	00 00 	addb	%al, (%rax)
       6:	00 00 	addb	%al, (%rax)
       8:	14 00 	adcb	$0, %al
       a:	00 00 	addb	%al, (%rax)
       c:	02 00 	addb	(%rax), %al
       e:	00 00 	addb	%al, (%rax)
      10:	fc 	cld
      11:	ff ff  <unknown>
      13:	ff ff  <unknown>
      15:	ff ff  <unknown>
      17:	ff 09 	decl	(%rcx)
      19:	00 00 	addb	%al, (%rax)
      1b:	00 00 	addb	%al, (%rax)
      1d:	00 00 	addb	%al, (%rax)
      1f:	00 04 00 	addb	%al, (%rax,%rax)
      22:	00 00 	addb	%al, (%rax)
      24:	05 00 00 00 fc 	addl	$4227858432, %eax
      29:	ff ff  <unknown>
      2b:	ff ff  <unknown>
      2d:	ff ff  <unknown>
      2f:	ff 10 	callq	*(%rax)
      31:	00 00 	addb	%al, (%rax)
      33:	00 00 	addb	%al, (%rax)
      35:	00 00 	addb	%al, (%rax)
      37:	00 15 00 00 00 02 	addb	%dl, 33554432(%rip)
      3d:	00 00 	addb	%al, (%rax)
      3f:	00 00 	addb	%al, (%rax)
      41:	00 00 	addb	%al, (%rax)
      43:	00 00 	addb	%al, (%rax)
      45:	00 00 	addb	%al, (%rax)
      47:	00  <unknown>
Disassembly of section .tdata._ZN3tls1A17h13af140b93a46e97E:
_ZN3tls1A17h13af140b93a46e97E:
       0:	2a  <unknown>

[philipc]

@bjorn3 Which tool did you use to dump the object file info?

Generated object for Windows x86-64

tls.o:	file format COFF-x86-64

architecture: x86_64
start address: 0x0000000000000000

RELOCATION RECORDS FOR [.text]:
0000000000000002 IMAGE_REL_AMD64_REL32 _tls_index
0000000000000016 IMAGE_REL_AMD64_SECREL _ZN3tls1A17h13af140b93a46e97E

Sections:
Idx Name          Size      Address          Type
  0 .text         00000000 0000000000000000 TEXT 
  1 .data         00000000 0000000000000000 DATA 
  2 .bss          00000000 0000000000000000 BSS
  3 .text         0000001b 0000000000000000 TEXT 
  4 .tls$         00000001 0000000000000000 DATA 

SYMBOL TABLE:
[ 0](sec  1)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .text
AUX scnlen 0x0 nreloc 0 nlnno 0 checksum 0x0 assoc 1 comdat 0
[ 2](sec  2)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .data
AUX scnlen 0x0 nreloc 0 nlnno 0 checksum 0x0 assoc 2 comdat 0
[ 4](sec  3)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .bss
AUX scnlen 0x0 nreloc 0 nlnno 0 checksum 0x0 assoc 3 comdat 0
[ 6](sec  4)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .text
AUX scnlen 0x1b nreloc 2 nlnno 0 checksum 0xe244a0f4 assoc 4 comdat 1
[ 8](sec  4)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x00000000 _ZN3tls8__get_it17h59d6925afa6bde3cE
[ 9](sec  5)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .tls$
AUX scnlen 0x1 nreloc 0 nlnno 0 checksum 0xdbbbc9d6 assoc 5 comdat 1
[11](sec  5)(fl 0x00)(ty   0)(scl   3) (nx 0) 0x00000000 _ZN3tls1A17h13af140b93a46e97E
[12](sec -1)(fl 0x00)(ty   0)(scl   3) (nx 0) 0x00000000 @feat.00
[13](sec  0)(fl 0x00)(ty   0)(scl   2) (nx 0) 0x00000000 _tls_index
[14](sec -2)(fl 0x00)(ty   0)(scl  67) (nx 1) 0x00000000 .file
AUX tls.3a1fbbbh-cgu.0
Export Table:

Disassembly of section .text:
0000000000000000 _ZN3tls8__get_it17h59d6925afa6bde3cE:
       0:	8b 05 00 00 00 00 	movl	(%rip), %eax
		0000000000000002:  IMAGE_REL_AMD64_REL32	_tls_index
       6:	65 48 8b 0c 25 58 00 00 00 	movq	%gs:88, %rcx
       f:	48 8b 04 c1 	movq	(%rcx,%rax,8), %rax
      13:	48 8d 80 00 00 00 00 	leaq	(%rax), %rax
		0000000000000016:  IMAGE_REL_AMD64_SECREL	_ZN3tls1A17h13af140b93a46e97E
      1a:	c3 	retq
Disassembly of section .tls$:
0000000000000000 _ZN3tls1A17h13af140b93a46e97E:
       0:	2a  <unknown>

[bjorn3]

Which tool did you use to dump the object file info?

https://github.com/m4b/bingrep

[bjorn3]

I found documentation for ELF TLS: https://akkadia.org/drepper/tls.pdf

[bjorn3]

Opened wip pr bytecodealliance/cranelift#1174 for ELF TLS.