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linux_exec_hint_x86_64.c (752B)

      1 /* x86_64 Linux runtime-alias hint: place the runtime alias in the low 2 GiB
      2  * (MAP_32BIT) so that direct call/jmp displacements from text (typically
      3  * loaded around 0x400000 under PIE) reach without large-code-model thunks.
      4  * The write alias has no PC-relative usage and can live anywhere. */
      5 
      6 #include <stddef.h>
      7 #include <stdint.h>
      8 #include <sys/mman.h>
      9 
     10 #include "env_posix.h"
     11 
     12 int env_execmem_runtime_extra_flags(void) { return MAP_32BIT; }
     13 
     14 void* env_execmem_low_runtime_hint(size_t size) {
     15   static uintptr_t g = 0x40000000u;
     16   uintptr_t p = g;
     17   uintptr_t step = (uintptr_t)((size + 0xffffu) & ~(size_t)0xffffu);
     18   if (step < 0x10000u) step = 0x10000u;
     19   g = p + step + 0x10000u;
     20   if (g > 0x78000000u) g = 0x40000000u;
     21   return (void*)p;
     22 }