[ASan] Added intermediate functions between assembly and __asan_report.* to avoid link errors.

[kstoimenov]

Summary

Instead of calling asan_report.* directly from assembly code they have been replaced with corresponding asan_report.*_asm function, which call asan_report.*. All asan_report.* are now undefined weak symbols, which allows DSOs to link when z defs is used.

[morehouse]

LGTM

[MaskRay]

Other than __asan_report.*_asm intermediate functions the @PLT is removed from the assembly code.

The @PLT modifier does not matter for x86-64. @PLT for jmp/call is ignored anyway since the integrated assembler switched from R_X86_64_PC32 to R_X86_64_PLT32.

Added intermediate functions between assembly and __asan_report.* to avoid link errors.

Do you mind more information to clarify how the link error (which diagnostic?) is avoided?

[MaskRay]

compiler-rt/lib/asan/asan_rtl_static.cpp

20

WEAK_DEF may be misleading because the declared symbol (__asan_report_load1) is not a definition.

Consider just write extern "C" SANITIZER_WEAK_ATTRIBUTE

[MaskRay]

• https://reviews.llvm.org/D107850 outlined some instrumented code sequences to __asan_check_* functions
• -fsanitize-address-outline-instrumentation -mllvm -asan-optimize-callbacks=1 teaches the asan instrumentation to call __asan_check_*
• https://reviews.llvm.org/D114558 implemented these __asan_check_* functions in libclang_rt.asan-static.a. They were later changed to hidden visibility to avoid PLT
• A __asan_check_* function may call __asan_report_* in libclang_rt.asan.a

When linking a shared object, libclang_rt.asan-static.a may bring in some resolved undefined symbols, causing a --no-undefined (-z defs) link to fail.

This patch changes the symbol table entries

% egrep 'load8|load_add_8_RAX' asan_static.txt
    15: 000000000000011a     0 NOTYPE  LOCAL  DEFAULT    2 .fail_load_add_8_RAX
   227: 0000000000000108     0 FUNC    GLOBAL HIDDEN     2 __asan_check_load_add_8_RAX
   228: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT  UND __asan_report_load8

to

% egrep 'load8|load_add_8_RAX' asan_static.new.txt
     5: 0000000000000000     0 SECTION LOCAL  DEFAULT    9 .text.__asan_report_load8_asm
    25: 0000000000000000     5 FUNC    GLOBAL HIDDEN     9 __asan_report_load8_asm
    26: 0000000000000000     0 NOTYPE  WEAK   DEFAULT  UND __asan_report_load8
    15: 000000000000011a     0 NOTYPE  LOCAL  DEFAULT    2 .fail_load_add_8_RAX
   227: 0000000000000108     0 FUNC    GLOBAL HIDDEN     2 __asan_check_load_add_8_RAX
   228: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT  UND __asan_report_load8_asm

Since the call to __asan_report_load8 is now weak, the linker will not error for --no-undefined (-z defs).
So, the patch LGTM, but it needs some clarification.

[MaskRay]

Added intermediate functions between assembly and __asan_report.* to avoid link errors.

The main difference is not intermediate functions, but weak references to functions defined in asan.a (e.g. __asan_report_load8) to fix --no-undefined linker errors.

[kstoimenov]

Fixed function def.

compiler-rt/lib/asan/asan_rtl_static.cpp

 //===-- asan_static_rtl.cpp -----------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file is a part of AddressSanitizer, an address sanity checker.
 //
 // Main file of the ASan run-time library.
 //===----------------------------------------------------------------------===//
 
 // This file is empty for now. Main reason to have it is workaround for Windows
 // build, which complains because no files are part of the asan_static lib.
+
+#include "sanitizer_common/sanitizer_common.h"
+
+#define REPORT_FUNCTION(Name)                                       \
+  extern "C" SANITIZER_WEAK_ATTRIBUTE void Name(__asan::uptr addr); \
+  extern "C" void Name##_asm(uptr addr) { Name(addr); }
+
+namespace __asan {
+
+REPORT_FUNCTION(__asan_report_load1)
+REPORT_FUNCTION(__asan_report_load2)
+REPORT_FUNCTION(__asan_report_load4)
+REPORT_FUNCTION(__asan_report_load8)
+REPORT_FUNCTION(__asan_report_load16)
+REPORT_FUNCTION(__asan_report_store1)
+REPORT_FUNCTION(__asan_report_store2)
+REPORT_FUNCTION(__asan_report_store4)
+REPORT_FUNCTION(__asan_report_store8)
+REPORT_FUNCTION(__asan_report_store16)
+
+}  // namespace __asan

compiler-rt/lib/asan/asan_rtl_x86_64.S

 CLABEL(reg, op, 1, i): ;\
         push   %rcx ;\
         mov    %##reg,%rcx ;\
         and    $0x7,%ecx ;\
         cmp    %r10d,%ecx ;\
         pop    %rcx ;\
         jl     RLABEL(reg, op, 1, i);\
         mov    %##reg,%rdi ;\
-        jmp    __asan_report_##op##1@PLT ;\
+        jmp    __asan_report_##op##1_asm ;\
 
 #define ASAN_MEMORY_ACCESS_EXTRA_CHECK_2(reg, op, i) \
 CLABEL(reg, op, 2, i): ;\
         push   %rcx ;\
         mov    %##reg,%rcx ;\
         and    $0x7,%ecx ;\
         add    $0x1,%ecx ;\
         cmp    %r10d,%ecx ;\
         pop    %rcx ;\
         jl     RLABEL(reg, op, 2, i);\
         mov    %##reg,%rdi ;\
-        jmp    __asan_report_##op##2@PLT ;\
+        jmp    __asan_report_##op##2_asm ;\
 
 #define ASAN_MEMORY_ACCESS_EXTRA_CHECK_4(reg, op, i) \
 CLABEL(reg, op, 4, i): ;\
         push   %rcx ;\
         mov    %##reg,%rcx ;\
         and    $0x7,%ecx ;\
         add    $0x3,%ecx ;\
         cmp    %r10d,%ecx ;\
         pop    %rcx ;\
         jl     RLABEL(reg, op, 4, i);\
         mov    %##reg,%rdi ;\
-        jmp    __asan_report_##op##4@PLT ;\
+        jmp    __asan_report_##op##4_asm ;\
 
 #define ASAN_MEMORY_ACCESS_CALLBACK_ADD_1(reg, op) \
 BEGINF(reg, op, 1, add) ;\
         ASAN_MEMORY_ACCESS_INITIAL_CHECK_ADD(reg, op, 1) ;\
         ASAN_MEMORY_ACCESS_EXTRA_CHECK_1(reg, op, add) ;\
 ENDF
 
 #define ASAN_MEMORY_ACCESS_CALLBACK_ADD_2(reg, op) \
#define ASAN_MEMORY_ACCESS_CHECK_ADD(reg, op, s, c) \
         shr    $0x3,%r10 ;\
         ##c    $0x0,ASAN_SHADOW_OFFSET_CONST(%r10) ;\
         jne    FLABEL(reg, op, s, add) ;\
         retq  ;\
 
 #define ASAN_MEMORY_ACCESS_FAIL(reg, op, s, i) \
 FLABEL(reg, op, s, i): ;\
         mov    %##reg,%rdi ;\
-        jmp    __asan_report_##op##s@PLT;\
+        jmp    __asan_report_##op##s##_asm;\
 
 #define ASAN_MEMORY_ACCESS_CALLBACK_ADD_8(reg, op) \
 BEGINF(reg, op, 8, add) ;\
         ASAN_MEMORY_ACCESS_CHECK_ADD(reg, op, 8, cmpb) ;\
         ASAN_MEMORY_ACCESS_FAIL(reg, op, 8, add) ;\
 ENDF
 
 #define ASAN_MEMORY_ACCESS_CALLBACK_ADD_16(reg, op) \