Re: [REGRESSION] "efi: efistub: Convert into static library" and preparation patches

[Ard Biesheuvel]

> On 4 sep. 2014, at 12:48, Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxx> wrote:
> 
> Op 03-09-14 om 21:57 schreef Ard Biesheuvel:
>> On 3 September 2014 19:59, Matt Fleming <matt@xxxxxxxxxxxxxxxxx> wrote:
>>> On Wed, 03 Sep, at 05:37:26PM, Ard Biesheuvel wrote:
>>>> Will do, thanks.
>>>> 
>>>> @Matt: so there is two ways to fix this, the patch above addressing
>>>> this single instance, and alternatively, adding a #pragma GCC
>>>> visiblilty push(hidden) to all .c files under libstub/, *before* the
>>>> #includes. The latter would catch future problems regarding newly
>>>> introduced global variables, but it may be a bit overkill in this
>>>> case, as libstub is not expected to be in flux in the foreseeable
>>>> future.
>>>> 
>>>> Any preferences?
>>> Any reason we can't reuse the existing GOT fixup code in the early x86
>>> boot code? We're not executing it before the EFI boot stub atm, which is
>>> the reason Maarten is hitting these difficulties.
>> I guess that is likely to work, I just wasn't aware it existed :-)
>> I think adding another visibility(hidden) attribute or 2 would
>> complete eliminate the need for GOT fixups, but I guess that is more
>> sensitive to compiler versions being recent enough etc.
>> The attached (build tested only) patch eliminates all GOT relocations
>> under boot/compressed for a 64-bit EFI stub build.
>> 
>>> Maarten, does the following help?
>>> 
>>> If not, Ard please go ahead with option #2 above. Overkill yes, but I've
>>> done the single __attribute__() hacks in other projects and someone
>>> (usually me) always eventually forgets to tag some instance.
>> It appears we just got lucky on arm64, since we don't have any global
>> variables, but the issue does exist there as well.
> FWIW, visibility pushing doesn't seem to work for functions declared with extern.

Are you sure you are seeing GOT entries being generated for functions? Normally, these are resolved via PLT entries, and those usually don't result in GOT entries to be allocated unless the branch target is unknown at link time.


> Following seems to get rid of all GOTPCREL:
> ---
> diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h
> index bd49ec61255c..221da1e53d87 100644
> --- a/arch/x86/boot/boot.h
> +++ b/arch/x86/boot/boot.h
> @@ -298,8 +298,8 @@ int check_cpu(int *cpu_level_ptr, int *req_level_ptr, u32 **err_flags_ptr);
> int validate_cpu(void);
> 
> /* early_serial_console.c */
> -extern int early_serial_base;
> -void console_init(void);
> +extern __attribute__((__visibility__("hidden"))) int early_serial_base;
> +__attribute__((__visibility__("hidden"))) void console_init(void);
> 
> /* edd.c */
> void query_edd(void);
> diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
> index 24e3e569a13c..23ac047fd23e 100644
> --- a/arch/x86/boot/compressed/misc.h
> +++ b/arch/x86/boot/compressed/misc.h
> @@ -30,9 +30,10 @@
> #endif
> 
> /* misc.c */
> -extern memptr free_mem_ptr;
> -extern memptr free_mem_end_ptr;
> -extern struct boot_params *real_mode;        /* Pointer to real-mode data */
> +extern __attribute__((__visibility__("hidden"))) memptr free_mem_ptr;
> +extern __attribute__((__visibility__("hidden"))) memptr free_mem_end_ptr;
> +extern __attribute__((__visibility__("hidden"))) struct boot_params *real_mode;        /* Pointer to real-mode data */
> +
> void __putstr(const char *s);
> #define error_putstr(__x)  __putstr(__x)
> 
> @@ -75,7 +76,7 @@ unsigned char *choose_kernel_location(unsigned char *input,
> 
> #ifdef CONFIG_EARLY_PRINTK
> /* early_serial_console.c */
> -extern int early_serial_base;
> +__attribute__((__visibility__("hidden"))) int early_serial_base;
> void console_init(void);
> #else
> static const int early_serial_base;
> diff --git a/arch/x86/boot/cpuflags.h b/arch/x86/boot/cpuflags.h
> index ea97697e51e4..d01fcf94ece6 100644
> --- a/arch/x86/boot/cpuflags.h
> +++ b/arch/x86/boot/cpuflags.h
> @@ -10,8 +10,8 @@ struct cpu_features {
>    u32 flags[NCAPINTS];
> };
> 
> -extern struct cpu_features cpu;
> -extern u32 cpu_vendor[3];
> +__attribute__((visibility("hidden"))) extern struct cpu_features cpu;
> +__attribute__((visibility("hidden"))) extern u32 cpu_vendor[3];
> 
> int has_eflag(unsigned long mask);
> void get_cpuflags(void);
> diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
> index 044a2fd3c5fe..8725d85f1903 100644
> --- a/arch/x86/include/asm/efi.h
> +++ b/arch/x86/include/asm/efi.h
> @@ -178,7 +178,7 @@ struct efi_config {
>    bool is64;
> } __packed;
> 
> -extern struct efi_config *efi_early;
> +extern __attribute__((visibility("hidden"))) struct efi_config *efi_early;
> 
> #define efi_call_early(f, ...)                        \
>    efi_early->call(efi_early->f, __VA_ARGS__);
> 
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