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gh-91048: Prevent optimizing away the asyncio debug offsets structure on Windows #132963

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pablogsal merged 3 commits into from
Apr 25, 2025
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gh-91048: Prevent optimizing away the asyncio debug offsets structure on Windows #132963

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gh-91048: Prevent optimizing away the asyncio debug offsets structure…
pablogsal Apr 25, 2025
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pablogsal Apr 25, 2025
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Update Modules/_asynciomodule.c
pablogsal Apr 25, 2025
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gh-91048: Prevent optimizing away the asyncio debug offsets structure… 
… on Windows

To avoid having the debug sections being optimised away by the compiler
we use  __attribute__((used)) on gcc and clang but in Windows this is
not supported by the Microsoft compiler and there is no equivalent flag.
Unfortunately Windows offers almost no alternative other than exporting
the symbol in the dynamic table or using it somehow.
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pablogsal committed Apr 25, 2025
commit 4e99743f01f27f8c456cfaa8d736d8684cb01a0b
10 changes: 10 additions & 0 deletions Modules/_asynciomodule.c
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Expand Up @@ -185,6 +185,12 @@ typedef struct {
/* Counter for autogenerated Task names */
uint64_t task_name_counter;

#ifdef MS_WINDOWS
/* Pointer to the asyncio debug offset to avoid it to be optimized away
by the compiler in Windows (other platforms don't need this) */
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void *debug_offsets;

@chris-eibl chris-eibl Apr 25, 2025

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Then we'd even do not need the __attribute__((used)) any longer in the GENERATE_DEBUG_SECTION macros.
But it doesn't hurt either - so let's keep it?

@pablogsal pablogsal Apr 25, 2025

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Yeah I still prefer to keep it

#endif
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} asyncio_state;

static inline asyncio_state *
Expand Down Expand Up @@ -4320,6 +4326,10 @@ module_init(asyncio_state *state)
goto fail;
}

#ifdef MS_WINDOWS
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state->debug_offsets = &_AsyncioDebug;
#endif

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Py_DECREF(module);
return 0;

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