SD library: reduce stack size requirement by 4k by moving work buffer to heap #6745
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…er to heap. Better allocate the buffer for f_mkfs from the heap otherwise the stack requirement of this library is huge due to a work buffer allocated for f_mkfs in sdcard_mount. The work buffer is only needed if argument format_if_empty is set true (which is by default false). This change is quite important if you plan to use this library in a task. as now it increased the tasks stacks size by 4k, even this memory is never used if users are not aware of the large stack requirement during init this library may have other variables on stack that would have written memory outsides its range which can cause various side effects.
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Please put "SD library" somewhere in the PR title. |
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Description of Change
The stack requirement of this library is huge due to a work buffer allocated for f_mkfs in sdcard_mount. The work buffer is only needed if argument format_if_empty is set true (which is by default false) and the card was empty.
This change is quite important if you plan to use this library in a task. as now it increases the tasks stacks size by 4k, even this work memory is never used (due to format_if_empty is set false). If users are not aware of the large stack requirement during init this library they may have seen various side effects caused by the original code. the other variables in this function may have written addresses that were outside its valid stack range.
Tests scenarios
This issue was detected ESP32 when SD.begin was called from a task with a 2k stack (with format_if_empty set false).
Before this change either the stack of the task would have to been increased to 6k. Before it would show random crashed depending on time SD.begin was executed.