I saw directives after '%' in glibc's code: asm volatile ("movl %1, %0\n" : "=r" (a) : "i" (0x1234)); asm volatile ("movl %c1, %0\n" : "=r" (a) : "i" (0x1234)); asm volatile ("movl %P1, %0\n" : "=r" (a) : "i" (0x1234));
Currently I know the first line generates a imm load instruction (movl $0x1234, %eax), the second and the third line generate memory load operations (movl 0x1234, %eax). However, I don't know the difference between "%P" and "%c" directives. I read through section 5.37 and 5.38 of gcc.info (5.37 is Assembler Instructions with C Expression Operands; 5.38 is Constraints for `asm' Operands) but find nothing about them. Where to find documentation of them? Does gcc.info contain some information? -- Summary: Lack of documentation on asm extension Product: gcc Version: unknown Status: UNCONFIRMED Severity: minor Priority: P3 Component: c AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: pi3orama at gmail dot com http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43319