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Adding macros to push pinning roots #43

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merged 4 commits into from
Apr 29, 2024
Merged

Adding macros to push pinning roots #43

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94d6372
Adding macros to push roots that are not transitively pinned (only pi…
Mar 19, 2024
9a8d8ec
Renaming _RELAXED => _NO_TPIN
Mar 19, 2024
5f2b75e
Removing whitespace issues
Mar 19, 2024
e5e0bdc
Adding comment that explains how to push roots on the shadow stack th…
Apr 24, 2024
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7 changes: 7 additions & 0 deletions src/interpreter.c
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Original file line number Diff line number Diff line change
Expand Up @@ -51,7 +51,14 @@ extern void JL_GC_ENABLEFRAME(interpreter_state*) JL_NOTSAFEPOINT;

#else

#ifdef MMTK_GC
#define JL_GC_ENCODE_PUSHFRAME(n) ((((size_t)(n))<<3)|2)
// For roots that are not transitively pinned
#define JL_GC_ENCODE_PUSHFRAME_NO_TPIN(n) ((((size_t)(n))<<3)|6)
#else
#define JL_GC_ENCODE_PUSHFRAME(n) ((((size_t)(n))<<2)|2)
#define JL_GC_ENCODE_PUSHFRAME_NO_TPIN(n) JL_GC_ENCODE_PUSHFRAME(n)
#endif

#define JL_GC_PUSHFRAME(frame,locals,n) \
JL_CPPALLOCA(frame, sizeof(*frame)+(((n)+3)*sizeof(jl_value_t*))); \
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95 changes: 94 additions & 1 deletion src/julia.h
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Expand Up @@ -852,9 +852,40 @@ struct _jl_gcframe_t {

#define jl_pgcstack (jl_current_task->gcstack)

#ifndef MMTK_GC
#define JL_GC_ENCODE_PUSHARGS(n) (((size_t)(n))<<2)
#define JL_GC_ENCODE_PUSH(n) ((((size_t)(n))<<2)|1)

#define JL_GC_ENCODE_PUSHARGS_NO_TPIN(n) JL_GC_ENCODE_PUSHARGS(n)
#define JL_GC_ENCODE_PUSH_NO_TPIN(n) JL_GC_ENCODE_PUSH(n)
#else

// We use an extra bit (100) in the nroots value from the frame to indicate that the roots
// in the frame are/are not transitively pinning.
// There are currently 3 macros that encode passing nroots to the gcframe
// and they use the two lowest bits to encode information about what is in the frame (as below).
// To support the distinction between transtively pinning roots and non transitively pinning roots
// on the stack, we take another bit from nroots to encode information about whether or not to
// transitively pin the roots in the frame.
//
// So the ones that transitively pin look like:
// #define JL_GC_ENCODE_PUSHARGS(n) (((size_t)(n))<<3)
// #define JL_GC_ENCODE_PUSH(n) ((((size_t)(n))<<3)|1)
// #define JL_GC_ENCODE_PUSHFRAME(n) ((((size_t)(n))<<3)|2)
// and the ones that do not look like:
// #define JL_GC_ENCODE_PUSHARGS_NO_TPIN(n) (((size_t)(n))<<3|4)
// #define JL_GC_ENCODE_PUSH_NO_TPIN(n) ((((size_t)(n))<<3)|5)
// #define JL_GC_ENCODE_PUSHFRAME_NO_TPIN(n) ((((size_t)(n))<<3)|6)

// these are transitively pinning
#define JL_GC_ENCODE_PUSHARGS(n) (((size_t)(n))<<3)
#define JL_GC_ENCODE_PUSH(n) ((((size_t)(n))<<3)|1)

// these only pin the root object itself
#define JL_GC_ENCODE_PUSHARGS_NO_TPIN(n) (((size_t)(n))<<3|4)
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I don't know if Julia documents this anywhere. It is a good idea to explain what those bits are used for.

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There seems to be three different functions:

#define JL_GC_ENCODE_PUSHARGS(n)   (((size_t)(n))<<2)
#define JL_GC_ENCODE_PUSH(n)       ((((size_t)(n))<<2)|1)
#define JL_GC_ENCODE_PUSHFRAME(n)  ((((size_t)(n))<<2)|2)

I think they currently use 2 bits (<<2). It seems to indicate what stuff you'd push onto the shadow stack, but I might ask around so we can document this properly.

#define JL_GC_ENCODE_PUSH_NO_TPIN(n) ((((size_t)(n))<<3)|5)
#endif

#ifdef __clang_gcanalyzer__

// When running with the analyzer make these real function calls, that are
Expand Down Expand Up @@ -905,11 +936,11 @@ extern void JL_GC_POP() JL_NOTSAFEPOINT;
#define JL_GC_PUSH7(arg1, arg2, arg3, arg4, arg5, arg6, arg7) \
void *__gc_stkf[] = {(void*)JL_GC_ENCODE_PUSH(7), jl_pgcstack, arg1, arg2, arg3, arg4, arg5, arg6, arg7}; \
jl_pgcstack = (jl_gcframe_t*)__gc_stkf;

#define JL_GC_PUSH8(arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8) \
void *__gc_stkf[] = {(void*)JL_GC_ENCODE_PUSH(8), jl_pgcstack, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8}; \
jl_pgcstack = (jl_gcframe_t*)__gc_stkf;


#define JL_GC_PUSHARGS(rts_var,n) \
rts_var = ((jl_value_t**)alloca(((n)+2)*sizeof(jl_value_t*)))+2; \
((void**)rts_var)[-2] = (void*)JL_GC_ENCODE_PUSHARGS(n); \
Expand All @@ -921,6 +952,68 @@ extern void JL_GC_POP() JL_NOTSAFEPOINT;

#endif

#ifdef MMTK_GC
// these are pinning roots: only the root object needs to be pinned as opposed to
// the functions above which are transitively pinning
#define JL_GC_PUSH1_NO_TPIN(arg1) \
void *__gc_stkf[] = {(void*)JL_GC_ENCODE_PUSH_NO_TPIN(1), jl_pgcstack, arg1}; \
jl_pgcstack = (jl_gcframe_t*)__gc_stkf;

#define JL_GC_PUSH2_NO_TPIN(arg1, arg2) \
void *__gc_stkf[] = {(void*)JL_GC_ENCODE_PUSH_NO_TPIN(2), jl_pgcstack, arg1, arg2}; \
jl_pgcstack = (jl_gcframe_t*)__gc_stkf;

#define JL_GC_PUSH3_NO_TPIN(arg1, arg2, arg3) \
void *__gc_stkf[] = {(void*)JL_GC_ENCODE_PUSH_NO_TPIN(3), jl_pgcstack, arg1, arg2, arg3}; \
jl_pgcstack = (jl_gcframe_t*)__gc_stkf;

#define JL_GC_PUSH4_NO_TPIN(arg1, arg2, arg3, arg4) \
void *__gc_stkf[] = {(void*)JL_GC_ENCODE_PUSH_NO_TPIN(4), jl_pgcstack, arg1, arg2, arg3, arg4}; \
jl_pgcstack = (jl_gcframe_t*)__gc_stkf;

#define JL_GC_PUSH5_NO_TPIN(arg1, arg2, arg3, arg4, arg5) \
void *__gc_stkf[] = {(void*)JL_GC_ENCODE_PUSH_NO_TPIN(5), jl_pgcstack, arg1, arg2, arg3, arg4, arg5}; \
jl_pgcstack = (jl_gcframe_t*)__gc_stkf;

#define JL_GC_PUSH6_NO_TPIN(arg1, arg2, arg3, arg4, arg5, arg6) \
void *__gc_stkf[] = {(void*)JL_GC_ENCODE_PUSH_NO_TPIN(6), jl_pgcstack, arg1, arg2, arg3, arg4, arg5, arg6}; \
jl_pgcstack = (jl_gcframe_t*)__gc_stkf;

#define JL_GC_PUSH7_NO_TPIN(arg1, arg2, arg3, arg4, arg5, arg6, arg7) \
void *__gc_stkf[] = {(void*)JL_GC_ENCODE_PUSH_NO_TPIN(7), jl_pgcstack, arg1, arg2, arg3, arg4, arg5, arg6, arg7}; \
jl_pgcstack = (jl_gcframe_t*)__gc_stkf;

#define JL_GC_PUSH8_NO_TPIN(arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8) \
void *__gc_stkf[] = {(void*)JL_GC_ENCODE_PUSH_NO_TPIN(8), jl_pgcstack, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8}; \
jl_pgcstack = (jl_gcframe_t*)__gc_stkf;

#define JL_GC_PUSHARGS_NO_TPIN(rts_var,n) \
rts_var = ((jl_value_t**)alloca(((n)+2)*sizeof(jl_value_t*)))+2; \
((void**)rts_var)[-2] = (void*)JL_GC_ENCODE_PUSHARGS_NO_TPIN(n); \
((void**)rts_var)[-1] = jl_pgcstack; \
memset((void*)rts_var, 0, (n)*sizeof(jl_value_t*)); \
jl_pgcstack = (jl_gcframe_t*)&(((void**)rts_var)[-2])
#else
// When not using MMTk, default to the stock functions
#define JL_GC_PUSH1_NO_TPIN(arg1) JL_GC_PUSH1(arg1)

#define JL_GC_PUSH2_NO_TPIN(arg1, arg2) JL_GC_PUSH2(arg1, arg2)

#define JL_GC_PUSH3_NO_TPIN(arg1, arg2, arg3) JL_GC_PUSH3(arg1, arg2, arg3)

#define JL_GC_PUSH4_NO_TPIN(arg1, arg2, arg3, arg4) JL_GC_PUSH4(arg1, arg2, arg3, arg4)

#define JL_GC_PUSH5_NO_TPIN(arg1, arg2, arg3, arg4, arg5) JL_GC_PUSH5(arg1, arg2, arg3, arg4, arg5)

#define JL_GC_PUSH6_NO_TPIN(arg1, arg2, arg3, arg4, arg5, arg6) JL_GC_PUSH6(arg1, arg2, arg3, arg4, arg5, arg6)

#define JL_GC_PUSH7_NO_TPIN(arg1, arg2, arg3, arg4, arg5, arg6, arg7) JL_GC_PUSH7(arg1, arg2, arg3, arg4, arg5, arg6, arg7)

#define JL_GC_PUSH8_NO_TPIN(arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8) JL_GC_PUSH8(arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8)

#define JL_GC_PUSHARGS_NO_TPIN(rts_var,n) JL_GC_PUSHARGS(rts_var,n)
#endif

JL_DLLEXPORT int jl_gc_enable(int on);
JL_DLLEXPORT int jl_gc_is_enabled(void);

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