On 2020-04-11 16:31 -0500, relliott--- via Gcc-help wrote:
> Hello,
>
> Thanks for your reply. I guess I don’t understand why this requires so much
> memory all at once. Is it not possible to write to the object file as the
> initializer is parsed?
A compiler doesn't write to object file. It only writes to assembly file.
Modern compilers are designed multi-layer so the parser (frontend) should not
output assembly (it's the job of the backend). And, doing that so will miss
optimizations. A simple code:
const int b[] = {0, 1, 2};
int foo(void)
{
int i, x = 0;
for (i = 0; i < 3; i++)
x += b[i];
return x;
}
The body of "foo" will be optimized to "return 3;" at -O2. If we wrote the
array content to assembly file and discarded the value in memory, this
optimization will be impossible.
"xxd" a binary file and then compile the result with a compiler is just like
"converting a .jpg to .png then back to .jpg". A smarter way:
ld -r -b binary some_big_binary_blob.bin -o some_big_binary_blob.o
There will be symbols _binary_some_big_binary_blob_bin_start,
_binary_some_big_binary_blob_end in some_big_binary_blob.o. Then it's possible
to access the content of the binary blob with:
extern const char _binary_some_big_binary_blob_bin_start;
extern const char _binary_some_big_binary_blob_bin_end;
int main(void)
{
const char *begin = &_binary_some_big_binary_blob_bin_start;
const char *end = &_binary_some_big_binary_blob_bin_end;
const char *p;
for (p = begin; p != end; p++)
play_with(*p);
}
--
Xi Ruoyao <xry111@xxxxxxxxxxxxxxxx>
School of Aerospace Science and Technology, Xidian University
