[Bug ld/27566] [RISC-V] relocation truncated to fit: R_RISCV_GPREL_I against aymbol

[nelsonc1225 at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=27566

Nelson Chu <nelsonc1225 at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |nelsonc1225 at sourceware dot 
org

--- Comment #1 from Nelson Chu <nelsonc1225 at sourceware dot org> ---
Hi Lifang,

thanks for reporting this.  I'm really curious how this happened, so I spend
some times to research how DATA_SEGMENT_ALIGN and DATA_SEGMENT_RELRO_END work
in the current GNU linker.  Consider the binutils doc,

* DATA_SEGMENT_ALIGN(maxpagesize, commonpagesize) =
[maxpagesize == commonpagesize]
(ALIGN(maxpagesize) + (. & (maxpagesize - 1)))
[maxpagesize != commonpagesize]
(ALIGN(maxpagesize)
 + ((. + commonpagesize - 1) & (maxpagesize - commonpagesize)))

* DATA_SEGMENT_RELRO_END(offset, exp)
When ‘-z relro’ option is not present, DATA_SEGMENT_RELRO_END does nothing,
otherwise DATA_SEGMENT_ALIGN is padded so that exp + offset is aligned to the
commonpagesize argument given to DATA_SEGMENT_ALIGN.


I only consider the default linker script here.  Besides, I do some minor
changes to your original example, to see how the DATA_*_ALIGN work.

nelson@LAPTOP-QFSGI1F2:~/test/pr27566$ cat tmp.s
        .option nopic
        .section        .rodata
        .align  10
        .globl hello_rodata
hello_rodata:
        .zero   0x10
        .section .init_array
        .globl padding_init_array
padding_init_array:
        .zero 0xfc
        .text
        .align  1
        .globl  main
main:
        lui     a5,%hi(hello_rodata)
        addi    a5,a5,%lo(hello_rodata)
nelson@LAPTOP-QFSGI1F2:~/test/pr27566$
~/binutils-dev/build-linux64-upstream/build-install/bin/riscv64-unknown-linux-gnu-as
tmp.s -o tmp.o

Therefore, consider four cases as follows,

1. norelro, maxpagesize=0x1000, commonpagesize=0x1000

nelson@LAPTOP-QFSGI1F2:~/test/pr27566$
~/binutils-dev/build-linux64-upstream/build-install/bin/riscv64-unknown-linux-gnu-ld
-z norelro -z max-page-size=0x1000 -z common-page-size=0x1000 tmp.o -M > map1
nelson@LAPTOP-QFSGI1F2:~/test/pr27566$ cat map1
...
.rodata         0x0000000000010400       0x10
 *(.rodata .rodata.* .gnu.linkonce.r.*)
 .rodata        0x0000000000010400       0x10 tmp.o
                0x0000000000010400                hello_rodata
...
0x0000000000011410                . = DATA_SEGMENT_ALIGN (CONSTANT
(MAXPAGESIZE), CONSTANT (COMMONPAGESIZE))
...
.init_array     0x0000000000011410       0xfc
...
0x000000000001150c                . = DATA_SEGMENT_RELRO_END (., 0x0)
.data           0x000000000001150c        0x0
...

DATA_SEGMENT_ALIGN should be
(ALIGN(0x1000) + (0x10410 & (0x1000 - 1)))
= 0x11000 + (0x10410 & 0xfff)
= 0x11410
And DATA_SEGMENT_RELRO_END = 0x11410 + 0xfc = 0x1150c.
So we need to reserve at most "MAXPAGESIZE" size.

2. relro, maxpagesize=0x1000, commonpagesize=0x1000

nelson@LAPTOP-QFSGI1F2:~/test/pr27566$
~/binutils-dev/build-linux64-upstream/build-install/bin/riscv64-unknown-linux-gnu-ld
-z relro -z max-page-size=0x1000 -z common-page-size=0x1000 tmp.o -M > map2
nelson@LAPTOP-QFSGI1F2:~/test/pr27566$ cat map2
...
.rodata         0x0000000000010400       0x10
 *(.rodata .rodata.* .gnu.linkonce.r.*)
 .rodata        0x0000000000010400       0x10 tmp.o
                0x0000000000010400                hello_rodata
...
0x0000000000011f04                . = DATA_SEGMENT_ALIGN (CONSTANT
(MAXPAGESIZE), CONSTANT (COMMONPAGESIZE))
...
.init_array     0x0000000000011f04       0xfc
...
0x0000000000012000                . = DATA_SEGMENT_RELRO_END (., 0x0)
...

This is same as above, but since "-z relro",
DATA_SEGMENT_RELRO_END = ALIGN(0x1150c, 0x1000) = 0x12000
DATA_SEGMENT_ALIGN = 0x12000 - 0xfc = 0x11f04
So we need to reserve at most "MAXPAGESIZE + COMMONPAGESIZE" size =
"2*MAXPAGESIZE".

3. norelro, maxpagesize=0x10000, commonpagesize=0x2000

nelson@LAPTOP-QFSGI1F2:~/test/pr27566$
~/binutils-dev/build-linux64-upstream/build-install/bin/riscv64-unknown-linux-gnu-ld
-z norelro -z max-page-size=0x10000 -z common-page-size=0x2000 tmp.o -M > map3
nelson@LAPTOP-QFSGI1F2:~/test/pr27566$ cat map3
...
.rodata         0x0000000000010400       0x10
 *(.rodata .rodata.* .gnu.linkonce.r.*)
 .rodata        0x0000000000010400       0x10 tmp.o
                0x0000000000010400                hello_rodata
...
0x0000000000020410                . = DATA_SEGMENT_ALIGN (CONSTANT
(MAXPAGESIZE), CONSTANT (COMMONPAGESIZE))
...
.init_array     0x0000000000020410       0xfc
...
0x000000000002050c                . = DATA_SEGMENT_RELRO_END (., 0x0)
...

DATA_SEGMENT_ALIGN =
(ALIGN(0x10000) + (0x10410 & (0x2000 - 1)))
= 0x20000 + (0x10410 & 0x1fff)
= 0x20410
DATA_SEGMENT_RELRO_END = 0x20410 + 0xfc = 0x2050c.
So we need to reserve at most "MAXPAGESIZE" size.

4. relro, maxpagesize=0x10000, commonpagesize=0x2000

nelson@LAPTOP-QFSGI1F2:~/test/pr27566$
~/binutils-dev/build-linux64-upstream/build-install/bin/riscv64-unknown-linux-gnu-ld
-z relro -z max-page-size=0x10000 -z common-page-size=0x2000 tmp.o -M > map4
nelson@LAPTOP-QFSGI1F2:~/test/pr27566$ cat map4
...
.rodata         0x0000000000010400       0x10
 *(.rodata .rodata.* .gnu.linkonce.r.*)
 .rodata        0x0000000000010400       0x10 tmp.o
                0x0000000000010400                hello_rodata
...
0x0000000000021f04                . = DATA_SEGMENT_ALIGN (CONSTANT
(MAXPAGESIZE), CONSTANT (COMMONPAGESIZE))
...
.init_array     0x0000000000021f04       0xfc
...
0x0000000000022000                . = DATA_SEGMENT_RELRO_END (., 0x0)
...

DATA_SEGMENT_RELRO_END = ALIGN(0x20410, 0x2000) = 0x22000
DATA_SEGMENT_ALIGN = 0x22000 - 0xfc = 0x21f04
So we need to reserve at most "MAXPAGESIZE + COMMONPAGESIZE" size.

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