On Wed, Oct 21, 2015 at 10:44:56 -0700, H.J. Lu wrote:
> On Wed, Oct 21, 2015 at 10:42 AM, Ilya Verbin <iver...@gmail.com> wrote:
> > On Wed, Oct 21, 2015 at 10:38:10 -0700, H.J. Lu wrote:
> >> On Wed, Oct 21, 2015 at 10:33 AM, Ilya Verbin <iver...@gmail.com> wrote:
> >> > H.J.,
> >> > Maybe linker should print some warning about joining writable +
> >> > nonwritable
> >> > sections? Here is a simple testcase:
> >> >
> >> > $ cat t1.s
> >> > .section ".AAA", "a"
> >> > .long 0x12345678
> >> > $ cat t2.s
> >> > .section ".AAA", "wa"
> >> > .long 0x12345678
> >> > $ as t1.s -o t1.o
> >> > $ as t2.s -o t2.o
> >> > $ ld -shared t1.o t2.o
> >> > $ ls -lh a.out
> >> > 2.1M a.out
> >> >
> >>
> >> Does linker make AAA writable? If yes, linker does what it
> >> is told.
> >
> > Yes, it makes it writable, but why it also makes this?
> >
> > [Nr] Name Type Address Offset
> > Size EntSize Flags Link Info Align
> > [ 0] NULL 0000000000000000 00000000
> > 0000000000000000 0000000000000000 0 0 0
> > [ 1] .hash HASH 00000000000000b0 000000b0
> > 0000000000000028 0000000000000004 A 2 0 8
> > [ 2] .dynsym DYNSYM 00000000000000d8 000000d8
> > 0000000000000078 0000000000000018 A 3 2 8
> > [ 3] .dynstr STRTAB 0000000000000150 00000150
> > 0000000000000019 0000000000000000 A 0 0 1
> > [ 4] .AAA PROGBITS 0000000000000169 00000169
> > 0000000000000008 0000000000000000 WA 0 0 1
> > [ 5] .eh_frame PROGBITS 0000000000000178 00000178
> > 0000000000000000 0000000000000000 A 0 0 8
> > [ 6] .dynamic DYNAMIC 0000000000200178 00200178 <--
> > ???
> > 00000000000000b0 0000000000000010 WA 3 0 8
> > [ 7] .shstrtab STRTAB 0000000000000000 00200380
> > 0000000000000049 0000000000000000 0 0 1
> > [ 8] .symtab SYMTAB 0000000000000000 00200228
> > 0000000000000120 0000000000000018 9 9 8
> > [ 9] .strtab STRTAB 0000000000000000 00200348
> > 0000000000000038 0000000000000000 0 0 1
> >
>
> Linker groups input sections by section name and ors section
> flags.
Could you please help figure out how this number 0x200178 is calculated?
ld -verbose doesn't show anything helpful. It seems that something goes wrong
during section-to-segment mapping, because when both .AAA have "wa" flags, we
got small binary with 2 LOAD segments:
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flags Align
LOAD 0x0000000000000000 0x0000000000000000 0x0000000000000000
0x00000000000001a8 0x00000000000001a8 R 200000
LOAD 0x00000000000001a8 0x00000000002001a8 0x00000000002001a8
0x00000000000000b8 0x00000000000000b8 RW 200000
But when one .AAA has "a" flag, and another .AAA has "wa" flag, we got huge
binary with only one big LOAD segment:
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flags Align
LOAD 0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000200228 0x0000000000200228 RW 200000
BTW, gold produces small binary in both cases.
Thanks,
-- Ilya
