Sanitizer/MIPS: fix build fail on pre-R6

[wzssyqa]

Summary

On MIPS pre-R6, instruction b can only work within 64KiB,
which is not enough now.

We need the help of GOT.
For __mips64, we can get GOT by:

lui $t8, %hi(%neg(%gp_rel(SANITIZER_STRINGIFY(TRAMPOLINE(func)))))
daddu $t8, $t8, $t9
daddiu $t8, $t8, %hi(%neg(%gp_rel(SANITIZER_STRINGIFY(TRAMPOLINE(func)))))

And then get the address of __interceptor_func, and jump to it

ld $t9, %got_disp(__interceptor_" SANITIZER_STRINGIFY(func) ")($t8)
jr $t9

MIPS/O32 has .cpload, which can help to generate 3 instructions to get GOT.

MIPSr6 has instruction bc, which can jump long enough.

[MaskRay]

This large pile of mips code makes me nervous. What I really want is to eliminate code related to some older mips ports.
For example, just claim that defined(__mips__) && __mips_isa_rev < 6 is not supported for sanitizers.

[jrtc27]

Why not define a SANITIZER_TAIL_CALL(sym) that expands to the assembly string to tail call sym? Give it the default implementation of the current ASM_TAIL_CALL sym and then add MIPS overrides as needed. That should drastically reduce the amount of boilerplate; this copy-pasta is not good.

[wzssyqa]

In D158491#4607577, @MaskRay wrote:

This large pile of mips code makes me nervous. What I really want is to eliminate code related to some older mips ports.
For example, just claim that defined(__mips__) && __mips_isa_rev < 6 is not supported for sanitizers.

Pre-R6 is what currently widely used mostly.
I wish it can be supported.

[jrtc27]

Please upload patches with full context per https://llvm.org/docs/DeveloperPolicy.html#making-and-submitting-a-patch

compiler-rt/lib/sanitizer_common/sanitizer_asm.h

48

One space not two

49

Should mips be removed?

59

One space for these

60

No spaces before \n

62

Why $t8 rather than another temporary or $gp?

[wzssyqa]

compiler-rt/lib/sanitizer_common/sanitizer_asm.h

49

Should mips be removed?

No. Since ASM_INTERCEPTOR_TRAMPOLINE uses it.
For full asm functions, like vfork, the distance of these 2 functions is quite near.
b is enough for it.
See https://reviews.llvm.org/D158268

62

Why $t8 rather than another temporary or $gp?

In fact, I don't know. I tested with $gp, while something wrong (segfault) always happen.
I have no idea why...

[jrtc27]

Ah, I went and reminded myself of the MIPS ABI. N32/N64 has GP as call-preserved. O32 has GP as call-preserved for non-PIC, call-clobbered for PIC.

Also %got_disp forces eager binding and is a function pointer. If this can be adapted to use %call16 that would be better. I assume there's something similar for O32 but am not familiar enough with it.

[wzssyqa]

ping

[sylvestre.ledru]

@MaskRay do you think it could be merged now ? thanks
i have been told that it is necessary for Debian

[wzssyqa]

ping. This problem affects gcc now.

compiler-rt/lib/interception/interception.h

#  define DECLARE_WRAPPER(ret_type, func, ...)                                 \
      asm(                                                                      \
        ".text\n"                                                               \
        __ASM_WEAK_WRAPPER(func)                                                \
        ".set " #func ", " SANITIZER_STRINGIFY(TRAMPOLINE(func)) "\n"           \
        ".globl " SANITIZER_STRINGIFY(TRAMPOLINE(func)) "\n"                    \
        ".type  " SANITIZER_STRINGIFY(TRAMPOLINE(func)) ", %function\n"         \
        SANITIZER_STRINGIFY(TRAMPOLINE(func)) ":\n"                             \
        SANITIZER_STRINGIFY(CFI_STARTPROC) "\n"                                 \
-       SANITIZER_STRINGIFY(ASM_TAIL_CALL) " __interceptor_"                    \
-         SANITIZER_STRINGIFY(ASM_PREEMPTIBLE_SYM(func)) "\n"                   \
+       C_ASM_TAIL_CALL(SANITIZER_STRINGIFY(TRAMPOLINE(func)),                  \
+                       "__interceptor_"                                        \
+                         SANITIZER_STRINGIFY(ASM_PREEMPTIBLE_SYM(func))) "\n"  \
        SANITIZER_STRINGIFY(CFI_ENDPROC) "\n"                                   \
        ".size  " SANITIZER_STRINGIFY(TRAMPOLINE(func)) ", "                    \
             ".-" SANITIZER_STRINGIFY(TRAMPOLINE(func)) "\n"                    \
      );
 # else  // ASM_INTERCEPTOR_TRAMPOLINE_SUPPORT
 // Some architectures cannot implement efficient interceptor trampolines with
 // just a plain jump due to complexities of resolving a preemptible symbol. In
 // those cases, revert to just this scheme:

compiler-rt/lib/sanitizer_common/sanitizer_asm.h

 # define CFI_OFFSET(reg, n)
 # define CFI_DEF_CFA_REGISTER(reg)
 # define CFI_DEF_CFA(reg, n)
 # define CFI_RESTORE(reg)
 #endif
 
 #if defined(__x86_64__) || defined(__i386__) || defined(__sparc__)
 # define ASM_TAIL_CALL jmp
+#elif defined(__mips__) && __mips_isa_rev >= 6
+# define ASM_TAIL_CALL bc
 #elif defined(__arm__) || defined(__aarch64__) || defined(__mips__) || \
     defined(__powerpc__) || defined(__loongarch_lp64)
 # define ASM_TAIL_CALL b
 #elif defined(__s390__)
 # define ASM_TAIL_CALL jg
 #elif defined(__riscv)
 # define ASM_TAIL_CALL tail
 #endif
 
+#if defined(__mips64) && __mips_isa_rev < 6
+# define C_ASM_TAIL_CALL(tfunc, ifunc)                        \
+    "lui $t8, %hi(%neg(%gp_rel(" tfunc ")))\n"                \
+    "daddu $t8, $t8, $t9\n"                                   \
+    "daddu $t8, $t8, %lo(%neg(%gp_rel(" tfunc ")))\n"         \
+    "ld $t9, %got_disp(" ifunc ")($t8)\n"                     \
+    "jr $t9\n"
+#elif defined(__mips__) && __mips_isa_rev < 6
+# define C_ASM_TAIL_CALL(tfunc, ifunc)                        \
+    ".set    noreorder\n"                                     \
+    ".cpload $t9\n"                                           \
+    ".set    reorder\n"                                       \
+    "lw $t9, %got(" ifunc ")($gp)\n"                          \
+    "jr $t9\n"
+#elif defined(ASM_TAIL_CALL)
+#  define C_ASM_TAIL_CALL(tfunc, ifunc) \
+    SANITIZER_STRINGIFY(ASM_TAIL_CALL) " " ifunc
+#endif
+
 #if defined(__ELF__) && defined(__x86_64__) || defined(__i386__) || \
     defined(__riscv)
 # define ASM_PREEMPTIBLE_SYM(sym) sym@plt
 #else
 # define ASM_PREEMPTIBLE_SYM(sym) sym
 #endif
 
 #if !defined(__APPLE__)