Re: [Xen-devel] [PATCH v2] make use of .startof.() and .sizeof.() assembler expressions

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 30.08.16 at 14:50, <julien.grall@xxxxxxx> wrote:
> On 24/08/16 08:44, Jan Beulich wrote:
>> --- a/xen/arch/arm/device.c
>> +++ b/xen/arch/arm/device.c
>> @@ -21,8 +21,8 @@
>>  #include <xen/errno.h>
>>  #include <xen/lib.h>
>>
>> -extern const struct device_desc _sdevice[], _edevice[];
>> -extern const struct acpi_device_desc _asdevice[], _aedevice[];
>> +extern const struct device_desc _sdevice[] asm(".startof.(.dev.info)");
>> +extern const struct device_desc _edevice[];
>>
>>  int __init device_init(struct dt_device_node *dev, enum device_class class,
>>                         const void *data)
>> @@ -51,6 +51,11 @@ int __init device_init(struct dt_device_
>>      return -EBADF;
>>  }
>>
>> +#ifdef CONFIG_ACPI
> 
> Why did you add the #ifdef CONFIG_ACPI here? It is not explained in the 
> commit message.

.startof.(section_which_not_exist) gives a linker error. And ld
doesn't add to the section table any sections mentioned in the
linker script, but without constituents.

> If you want to add it, it should be a separate patch and we should go 
> further by removing the section in the linker script.

While I don't think this needs to be broken out, it certainly can (but
then really there should have been a conditional like the one I
introduce from the beginning, to avoid having dead code in a non-
ACPI enabled binary).

>> --- a/xen/arch/arm/xen.lds.S
>> +++ b/xen/arch/arm/xen.lds.S
>> @@ -31,7 +31,6 @@ SECTIONS
>>    . = XEN_VIRT_START;
>>    _start = .;
>>    .text : /* XXX should be AT ( XEN_PHYS_START ) */ {
>> -        _stext = .;            /* Text section */
> 
> I don't see any removal of _stext in xen/arch/arm/alternative.c.

Why should that be removed? _stext doesn't cease to exist:

--- a/xen/include/xen/kernel.h
+++ b/xen/include/xen/kernel.h
@@ -71,24 +71,34 @@ extern char _start[], _end[], start[];
     (__p >= _start) && (__p < _end);            \
 })
 
-extern char _stext[], _etext[];
+extern const char _stext[] asm(".startof.(.text)");
+extern const char _etext[];
 #define is_kernel_text(p) ({                    \

Jan


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