Messages in this thread | | | From | Ammar Faizi <> | Subject | [RFC PATCH v2 0/8] Add dynamic memory allocator support for nolibc | Date | Tue, 22 Mar 2022 17:21:07 +0700 |
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Hi,
This is the v2 of RFC to add dynamic memory allocator support for nolibc.
## Background The need to allocate memory dynamically has become a requirement for the C programming language. Mainly it happens when the allocation size is determined at runtime. Many other use cases also do it when the object's lifetime is long-lived and needs to be recycled at runtime. Currently, the nolibc header doesn't support such a type of allocation. This series adds it.
## Implementation Add basic functions to manage dynamic memory allocation: - malloc() - calloc() - realloc() - free()
The allocator uses mmap() syscall to allocate the memory and uses munmap() syscall to free the allocated memory. The metadata to keep track the length for munmap-ing is simply defined as a struct below: ``` struct nolibc_heap { size_t len; char user_p[] __attribute__((__aligned__)); }; ``` malloc(), realloc() and calloc() return a pointer to `user_p`.
## Add my_syscall6() support for x86 32-bit. mmap() needs 6 arguments to work with. Not all architectures that nolibc supports have the my_syscall6() wrapper. This series also adds my_syscall6() wrapper support for i386.
Notes: On i386, the 6th argument of syscall goes in %ebp. However, both Clang and GCC cannot use %ebp in the clobber list and in the "r" constraint without using -fomit-frame-pointer. To make it always available for any kind of compilation, the below workaround is implemented.
For clang (the Assembly statement can't clobber %ebp): 1) Push the 6-th argument. 2) Push %ebp. 3) Load the 6-th argument from 4(%esp) to %ebp. 4) Do the syscall (int $0x80). 5) Pop %ebp (restore the old value of %ebp). 6) Add %esp by 4 (undo the stack pointer).
For GCC, fortunately it has a #pragma that can force a specific function to be compiled with -fomit-frame-pointer, so it can use "r"(var) where var is a variable bound to %ebp.
## Test The following simple program can be used to test this series:
https://gist.github.com/ammarfaizi2/db0af6aa0b95a0c7478bce64e349f021
@@ Changelog:
Link RFC v1: https://lore.kernel.org/lkml/20220320093750.159991-1-ammarfaizi2@gnuweeb.org/ RFC v1 -> RFC v2: - Add 2 new patches [PATCH 5/8] and [PATCH 7/8].
[PATCH 2/8] - Remove all `.global _start` for all build (GCC and Clang) instead of removing all `.weak _start` for clang build (Comment from Willy).
[PATCH 3/8] - Fix %ebp saving method. Don't use redzone, i386 doesn't have a redzone (comment from David and Alviro).
[PATCH 6/8] - Move container_of() and offsetof() macro to types.h with a separate patch (comment from Willy).
[PATCH 8/8] - Update strdup and strndup implementation, use strlen and strnlen to get the string length first (comment from Willy and Alviro). - Fix the subject line prefix, it was "tools/include/string: ", it should be "tools/nolibc/string: ". - Update the commit message.
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org> --- Ammar Faizi (8): tools/nolibc: x86-64: Update System V ABI document link tools/nolibc: Remove .global _start from the entry point code tools/nolibc: i386: Implement syscall with 6 arguments tools/nolibc/sys: Implement `mmap()` and `munmap()` tools/nolibc/types: Implement `offsetof()` and `container_of()` macro tools/nolibc/stdlib: Implement `malloc()`, `calloc()`, `realloc()` and `free()` tools/nolibc/string: Implement `strnlen()` tools/include/string: Implement `strdup()` and `strndup()`
tools/include/nolibc/arch-aarch64.h | 1 - tools/include/nolibc/arch-arm.h | 1 - tools/include/nolibc/arch-i386.h | 67 +++++++++++++++++++++++++++- tools/include/nolibc/arch-mips.h | 1 - tools/include/nolibc/arch-riscv.h | 1 - tools/include/nolibc/arch-x86_64.h | 3 +- tools/include/nolibc/stdlib.h | 68 +++++++++++++++++++++++++++++ tools/include/nolibc/string.h | 41 +++++++++++++++++ tools/include/nolibc/sys.h | 62 ++++++++++++++++++++++++++ tools/include/nolibc/types.h | 11 +++++ 10 files changed, 249 insertions(+), 7 deletions(-)
base-commit: 45abaed6ed05856556c60863f4cac429c92c431f -- Ammar Faizi
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