Patchwork [U-Boot,v1,6/7] MIPS: u-boot.lds: add relocation specific sections

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Submitter Daniel Schwierzeck
Date Feb. 9, 2013, 8:33 p.m.
Message ID <1360442010-7520-7-git-send-email-daniel.schwierzeck@gmail.com>
Download mbox | patch
Permalink /patch/219442/
State Superseded
Delegated to: Daniel Schwierzeck
Headers show

Comments

Daniel Schwierzeck - Feb. 9, 2013, 8:33 p.m.
From: Gabor Juhos <juhosg@openwrt.org>

This section contain the table needed for dynamic
relocation. Also provide symbols for the relocation
code to access the table.

Discard all sections which are not needed in the final
ELF binary and U-Boot image. Section .dynsym cannot be
discarded or GNU ld crashes otherwise. This section
will be stripped by GNU objcpy in a later patch.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
---
 arch/mips/cpu/u-boot.lds | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)
Gabor Juhos - Feb. 11, 2013, 10:48 a.m.
2013.02.09. 21:33 keltezéssel, daniel.schwierzeck@gmail.com írta:
> From: Gabor Juhos <juhosg@openwrt.org>
> 
> This section contain the table needed for dynamic
> relocation. Also provide symbols for the relocation
> code to access the table.
> 
> Discard all sections which are not needed in the final
> ELF binary and U-Boot image. Section .dynsym cannot be
> discarded or GNU ld crashes otherwise. This section
> will be stripped by GNU objcpy in a later patch.
> 
> Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
> Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
> ---
>  arch/mips/cpu/u-boot.lds | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/mips/cpu/u-boot.lds b/arch/mips/cpu/u-boot.lds
> index 4cd983a..cea9533 100644
> --- a/arch/mips/cpu/u-boot.lds
> +++ b/arch/mips/cpu/u-boot.lds
> @@ -70,7 +70,17 @@ SECTIONS
>  	. = ALIGN(4);
>  	__image_copy_end = .;
>  
> -	.bss : {
> +	.rel.dyn : {
> +		__rel_dyn_start = .;
> +		*(.rel.dyn)
> +		__rel_dyn_end = .;
> +	}
> +
> +	.dynsym : {
> +		*(.dynsym)
> +	}

This is not enough to avoid the binutils issue I have mentioned in the original
patch. The issue is present after applying this series.

The following example comes from the qemu_mips target compiled with the ELDK 5.3
toolchain:

> $ mips-linux-objdump --disassemble u-boot | grep bfc005[67]
> bfc00560:       00000000        nop
> bfc00564:       bfc31f74        cache   0x3,8052(s8)    <--- __rel_dyn_end

The offset of __rel_dyn_end:
0x0bfc31f74 - 0xbfc00000 = 0x31f74 = 204660

> bfc00568:       bfc30804        cache   0x3,2052(s8)
> bfc0056c:       bfc30804        cache   0x3,2052(s8)
> bfc00570:       bfc2fa70        cache   0x2,-1424(s8)
> bfc00574:       000001df        0x1df
> bfc00578 <in_ram>:
> bfc00578:       8d0bfffc        lw      t3,-4(t0)
> bfc0057c:       8d0cfff8        lw      t4,-8(t0)

> $ ls -l u-boot.bin
> -rw-r--r-- 1 juhosg root 204284 Feb 11 11:29 u-boot.bin

204660 - 204284 = 376 bytes are missing from the final u-boot.bin.

-Gabor
Daniel Schwierzeck - Feb. 11, 2013, 1:32 p.m.
2013/2/11 Gabor Juhos <juhosg@openwrt.org>:
> 2013.02.09. 21:33 keltezéssel, daniel.schwierzeck@gmail.com írta:
>> From: Gabor Juhos <juhosg@openwrt.org>
>>
>> This section contain the table needed for dynamic
>> relocation. Also provide symbols for the relocation
>> code to access the table.
>>
>> Discard all sections which are not needed in the final
>> ELF binary and U-Boot image. Section .dynsym cannot be
>> discarded or GNU ld crashes otherwise. This section
>> will be stripped by GNU objcpy in a later patch.
>>
>> Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
>> Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
>> ---
>>  arch/mips/cpu/u-boot.lds | 24 +++++++++++++++++++++++-
>>  1 file changed, 23 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/mips/cpu/u-boot.lds b/arch/mips/cpu/u-boot.lds
>> index 4cd983a..cea9533 100644
>> --- a/arch/mips/cpu/u-boot.lds
>> +++ b/arch/mips/cpu/u-boot.lds
>> @@ -70,7 +70,17 @@ SECTIONS
>>       . = ALIGN(4);
>>       __image_copy_end = .;
>>
>> -     .bss : {
>> +     .rel.dyn : {
>> +             __rel_dyn_start = .;
>> +             *(.rel.dyn)
>> +             __rel_dyn_end = .;
>> +     }
>> +
>> +     .dynsym : {
>> +             *(.dynsym)
>> +     }
>
> This is not enough to avoid the binutils issue I have mentioned in the original
> patch. The issue is present after applying this series.
>
> The following example comes from the qemu_mips target compiled with the ELDK 5.3
> toolchain:
>
>> $ mips-linux-objdump --disassemble u-boot | grep bfc005[67]
>> bfc00560:       00000000        nop
>> bfc00564:       bfc31f74        cache   0x3,8052(s8)    <--- __rel_dyn_end
>
> The offset of __rel_dyn_end:
> 0x0bfc31f74 - 0xbfc00000 = 0x31f74 = 204660
>
>> bfc00568:       bfc30804        cache   0x3,2052(s8)
>> bfc0056c:       bfc30804        cache   0x3,2052(s8)
>> bfc00570:       bfc2fa70        cache   0x2,-1424(s8)
>> bfc00574:       000001df        0x1df
>> bfc00578 <in_ram>:
>> bfc00578:       8d0bfffc        lw      t3,-4(t0)
>> bfc0057c:       8d0cfff8        lw      t4,-8(t0)
>
>> $ ls -l u-boot.bin
>> -rw-r--r-- 1 juhosg root 204284 Feb 11 11:29 u-boot.bin
>
> 204660 - 204284 = 376 bytes are missing from the final u-boot.bin.
>
> -Gabor
>

that's weird. Actually I checked after each patch if the *_end symbols
match the U-Boot binary size. Now I checked again with different
toolchains (gcc-4.[5,6,7], binutils-2.[21.53,22] and I have again that
binutils issue.

But all toolchains have one in common (tested with qemu_mips):
__rel_dyn_end - __rel_dyn_start = 0x1770
size from readelf = 0x15f8

Another problem is that your .deadcode workaround does not work
anymore for me. It does not matter how I arrange or drop the unneeded
sections, the size of .rel.dyn remains at 0x1770. I'll try to find
another solution.

Patch

diff --git a/arch/mips/cpu/u-boot.lds b/arch/mips/cpu/u-boot.lds
index 4cd983a..cea9533 100644
--- a/arch/mips/cpu/u-boot.lds
+++ b/arch/mips/cpu/u-boot.lds
@@ -70,7 +70,17 @@  SECTIONS
 	. = ALIGN(4);
 	__image_copy_end = .;
 
-	.bss : {
+	.rel.dyn : {
+		__rel_dyn_start = .;
+		*(.rel.dyn)
+		__rel_dyn_end = .;
+	}
+
+	.dynsym : {
+		*(.dynsym)
+	}
+
+	.bss __rel_dyn_start (OVERLAY) : {
 		__bss_start = .;
 		*(.sbss.*)
 		*(.bss.*)
@@ -78,4 +88,16 @@  SECTIONS
 		. = ALIGN(4);
 		__bss_end = .;
 	}
+
+	/DISCARD/ : {
+		*(.dynbss)
+		*(.dynstr)
+		*(.dynamic)
+		*(.interp)
+		*(.hash)
+		*(.gnu.*)
+		*(.plt)
+		*(.got.plt)
+		*(.rel.plt)
+	}
 }