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Prevent malloc from overwriting the stack #681

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Prevent malloc from overwriting the stack #681

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b3da8fa
Remove unused -nostdlib compile options
matthijskooijman Jul 19, 2022
d232b59
Replace _sbrk to make malloc fail when out of memory
matthijskooijman Jul 8, 2022
4460dbc
Let malloc leave some extra space for the stack
matthijskooijman Jul 19, 2022
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7 changes: 7 additions & 0 deletions cores/arduino/main.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -56,3 +56,10 @@ int main( void )

return 0;
}

// Ensure our version of sbrk is used by forcing a reference to it here
// (without this, an undefined reference only occurs later when linking
// newlib, and the dummy from libgloss/nosys will be used instead).
// This variable will be optimized away later.
extern "C" void *_sbrk(int);
void * force_reference_to_sbrk = (void*)&_sbrk;
23 changes: 23 additions & 0 deletions cores/arduino/sbrk.c
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Original file line number Diff line number Diff line change
@@ -0,0 +1,23 @@
#include <samd.h>
#include <stddef.h>
#include <errno.h>

/* How much free space to keep between the stack and the heap by malloc.
* Can be changed by the application at any time. */
size_t __malloc_margin = 64;

void *_sbrk(int incr)
{
extern char end; /* End of global variables, defined by the linker */
static char *brkval = &end ;
char *prev_brkval = brkval;

if (brkval + incr + __malloc_margin > (char *)__get_MSP()) {
/* Heap and stack collision */
errno = ENOMEM;
return (void*) -1;
}

brkval += incr ;
return (void*) prev_brkval;
}
4 changes: 2 additions & 2 deletions platform.txt
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Expand Up @@ -39,13 +39,13 @@ compiler.optimization_flags.debug=-Og -g3

compiler.path={runtime.tools.arm-none-eabi-gcc-7-2017q4.path}/bin/
compiler.c.cmd=arm-none-eabi-gcc
compiler.c.flags=-mcpu={build.mcu} -mthumb -c -g {compiler.optimization_flags} {compiler.warning_flags} -std=gnu11 -ffunction-sections -fdata-sections -nostdlib --param max-inline-insns-single=500 -MMD
compiler.c.flags=-mcpu={build.mcu} -mthumb -c -g {compiler.optimization_flags} {compiler.warning_flags} -std=gnu11 -ffunction-sections -fdata-sections --param max-inline-insns-single=500 -MMD
compiler.c.elf.cmd=arm-none-eabi-g++
compiler.c.elf.flags={compiler.optimization_flags} -Wl,--gc-sections -save-temps
compiler.S.cmd=arm-none-eabi-gcc
compiler.S.flags=-mcpu={build.mcu} -mthumb -c -g -x assembler-with-cpp -MMD
compiler.cpp.cmd=arm-none-eabi-g++
compiler.cpp.flags=-mcpu={build.mcu} -mthumb -c -g {compiler.optimization_flags} {compiler.warning_flags} -std=gnu++11 -ffunction-sections -fdata-sections -fno-threadsafe-statics -nostdlib --param max-inline-insns-single=500 -fno-rtti -fno-exceptions -MMD
compiler.cpp.flags=-mcpu={build.mcu} -mthumb -c -g {compiler.optimization_flags} {compiler.warning_flags} -std=gnu++11 -ffunction-sections -fdata-sections -fno-threadsafe-statics --param max-inline-insns-single=500 -fno-rtti -fno-exceptions -MMD
compiler.ar.cmd=arm-none-eabi-ar
compiler.ar.flags=rcs
compiler.objcopy.cmd=arm-none-eabi-objcopy
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