$uname -i
x86_64
$ uname -r
4.15.0-041500-generic
I am trying to compile that gets memory map of a system. The OSDev shows some code how that can be done.
The code is as follows:
// running in real mode may require:
__asm__(".code16gcc\n");
// SMAP entry structure
#include <stdint.h>
typedef struct SMAP_entry {
uint32_t BaseL; // base address uint64_t
uint32_t BaseH;
uint32_t LengthL; // length uint64_t
uint32_t LengthH;
uint32_t Type; // entry Type
uint32_t ACPI; // extended
}__attribute__((packed)) SMAP_entry_t;
// load memory map to buffer - note: regparm(3) avoids stack issues with gcc in real mode
int __attribute__((noinline)) __attribute__((regparm(3))) detectMemory(SMAP_entry_t* buffer, int maxentries)
{
uint32_t contID = 0;
int entries = 0, signature, bytes;
do
{
__asm__ __volatile__ ("int $0x15"
: "=a"(signature), "=c"(bytes), "=b"(contID)
: "a"(0xE820), "b"(contID), "c"(24), "d"(0x534D4150), "D"(buffer));
if (signature != 0x534D4150)
return -1; // error
if (bytes > 20 && (buffer->ACPI & 0x0001) == 0)
{
// ignore this entry
}
else {
buffer++;
entries++;
}
}
while (contID != 0 && entries < maxentries);
return entries;
}
// in your main routine - memory map is stored in 0000:1000 - 0000:2FFF for example
[...] {
[...]
SMAP_entry_t* smap = (SMAP_entry_t*) 0x1000;
const int smap_size = 0x2000;
int entry_count = detectMemory(smap, smap_size / sizeof(SMAP_entry_t));
if (entry_count == -1) {
// error - halt system and/or show error message
[...]
} else {
// process memory map
[...]
}
}
Obviously the code has to be compiled in 16 bit mode. So I used
gcc -m16 smapentry.c -o smap
This has resulted in a error which says.
usr/bin/x86_64-linux-gnu-ld: skipping incompatible /usr/lib/gcc/x86_64-linux-gnu/7/libgcc.a when searching for -lgcc
/usr/bin/x86_64-linux-gnu-ld: cannot find -lgcc
which means I have a 64 libgcc installed. For this reason, -m64 and -m32 works fine. only -m16 doesn't work. It looks like I need to install libgcc version to compile 16 bit code. Which library should I use?