On 1 August 2016 at 09:54, Shi, Steven <steven....@intel.com> wrote: >> On 1 August 2016 at 09:19, Shi, Steven >> <steven....@intel.com<mailto:steven....@intel.com>> wrote: >> >> >> >> >> >> The fact that it works does not make it safe. Having multiple fixups >> >> >> for the same symbol in the .reloc section is a problem, and so is >> >> >> reapplying GOTPCRELX to places where the original instruction has >> been >> >> >> replaced by the linker. >> >> >> >> >> > [Steven]: I still don't understand why there will be multiple fixups >> >> > for the >> >> same symbol in the .reloc section? >> >> > >> >> >> >> Remember this example >> >> >> >> >> > int n; >> >> >> > int f () { return n; } >> >> >> > int g () { return n; } >> >> >> > int h () { return n; } >> >> >> >> If every 'return n' results in a GOTPCREL relocation, how are you >> >> going to make sure that the GOT entry for 'n' is only fixed up a >> >> single time? >> > >> > [Steven]: the 'return n' will not result in relocation, but the 'int n' >> > will result >> in the relocation in GOT. The three 'return n' will point to the same 'int n' >> relocation item. So, we need only fixup 'int n' once, all three 'return n' >> will >> use the correct global 'n' value. >> >> Every 'return n' will result in a GOTPCREL relocation against n. And >> your code emits a relocation for the GOT entry every time. >> > [Steven]: I don't think so. please give a real case and offer its source code > to prove " Every 'return n' will result in a GOTPCREL relocation against n ". >
Compiling the code above using gcc -c -O -fpic /tmp/pie.c -o pie.o and dumping it using readelf -r pie.o gives me Relocation section '.rela.text' at offset 0x250 contains 3 entries: Offset Info Type Sym. Value Sym. Name + Addend 000000000003 000a0000002a R_X86_64_REX_GOTP 0000000000000004 n - 4 00000000000d 000a0000002a R_X86_64_REX_GOTP 0000000000000004 n - 4 000000000017 000a0000002a R_X86_64_REX_GOTP 0000000000000004 n - 4 ... -- Ard. _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel
