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Re: [PATCH 2/6] Align all sections to 4KB

  • To: Frediano Ziglio <freddy77@xxxxxxxxx>
  • From: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
  • Date: Sat, 13 Jun 2026 13:36:51 +0200
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  • Cc: Jan Beulich <jbeulich@xxxxxxxx>, Frediano Ziglio <frediano.ziglio@xxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Sat, 13 Jun 2026 11:37:03 +0000
  • Feedback-id: i1568416f:Fastmail
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Sat, Jun 13, 2026 at 12:20:53PM +0100, Frediano Ziglio wrote:
> On Thu, 11 Jun 2026 at 16:18, Jan Beulich <jbeulich@xxxxxxxx> wrote:
> >
> > On 11.06.2026 16:49, Frediano Ziglio wrote:
> > > On Wed, 10 Jun 2026 at 10:43, Jan Beulich <jbeulich@xxxxxxxx> wrote:
> > >>
> > >> On 06.06.2026 18:02, Frediano Ziglio wrote:
> > >>> Frediano
> > >>>
> > >>> On Fri, 5 Jun 2026 at 08:45, Jan Beulich <jbeulich@xxxxxxxx> wrote:
> > >>>>
> > >>>> On 04.06.2026 12:16, Frediano Ziglio wrote:
> > >>>>> On Tue, 2 Jun 2026 at 13:09, Jan Beulich <jbeulich@xxxxxxxx> wrote:
> > >>>>>> On 29.05.2026 17:35, Frediano Ziglio wrote:
> > >>>>>>> --- a/xen/arch/x86/xen.lds.S
> > >>>>>>> +++ b/xen/arch/x86/xen.lds.S
> > >>>>>>> @@ -162,8 +162,8 @@ SECTIONS
> > >>>>>>>         __note_gnu_build_id_end = .;
> > >>>>>>>    } PHDR(note) PHDR(text)
> > >>>>>>>  #elif defined(BUILD_ID_EFI)
> > >>>>>>> -  /* Workaround bug in binutils < 2.36 */
> > >>>>>>> -  . = ALIGN(32);
> > >>>>>>> +  /* align to satisfy UEFI CA memory mitigation */
> > >>>>>>> +  . = ALIGN(PAGE_SIZE);
> > >>>>>>>    DECL_SECTION(.buildid) {
> > >>>>>>>         __note_gnu_build_id_start = .;
> > >>>>>>>         *(.buildid)
> > >>>>>>> @@ -330,6 +330,7 @@ SECTIONS
> > >>>>>>>    __2M_rwdata_end = ALIGN(SECTION_ALIGN);
> > >>>>>>>
> > >>>>>>>  #ifdef EFI
> > >>>>>>> +  . = ALIGN(PAGE_SIZE);
> > >>>>>>>    .reloc ALIGN(4) : {
> > >>>>>>>      __base_relocs_start = .;
> > >>>>>>>      *(.reloc)
> > >>>>>>> @@ -355,6 +356,7 @@ SECTIONS
> > >>>>>>>    VIRT_START &= 0;
> > >>>>>>>    ALT_START &= 0;
> > >>>>>>>
> > >>>>>>> +  . = ALIGN(PAGE_SIZE);
> > >>>>>>>    .sbat (NOLOAD) : { *(.sbat) }
> > >>>>>>>  #elif defined(XEN_BUILD_EFI)
> > >>>>>>>    /*
> > >>>>>>
> > >>>>>> You say "all sections" in the title, yet this is not covering e.g. 
> > >>>>>> debug
> > >>>>>> info.
> > >>>>>
> > >>>>> I will change to "all loadable sections". debug sections are not
> > >>>>> loadable so they don't cause an issue.
> > >>>>
> > >>>> Please try to be precise there, as some aspects are subtle. As per my
> > >>>> understanding, like .reloc all .debug_* are loadable (and may be 
> > >>>> loaded).
> > >>>> The IMAGE_SCN_MEM_DISCARDABLE flag merely means they can be discarded 
> > >>>> at
> > >>>> a certain point after image loading (for .reloc in particular: after
> > >>>> relocations were processed).
> > >>>
> > >>> No, debug sections are not loadable, for instance, in a random
> > >>> executable I found:
> > >>>
> > >>> Sections:
> > >>> Idx Name          Size      VMA               LMA               File 
> > >>> off  Algn
> > >>>   0 .text         0000c7f8  0000000140001000  0000000140001000  
> > >>> 00000600  2**4
> > >>>                   CONTENTS, ALLOC, LOAD, READONLY, CODE, DATA
> > >>>   1 .data         00000250  000000014000e000  000000014000e000  
> > >>> 0000ce00  2**4
> > >>>                   CONTENTS, ALLOC, LOAD, DATA
> > >>>   2 .rdata        00002c70  000000014000f000  000000014000f000  
> > >>> 0000d200  2**4
> > >>>                   CONTENTS, ALLOC, LOAD, READONLY, DATA
> > >>>   3 .pdata        00000654  0000000140012000  0000000140012000  
> > >>> 00010000  2**2
> > >>>                   CONTENTS, ALLOC, LOAD, READONLY, DATA
> > >>>   4 .xdata        00000630  0000000140013000  0000000140013000  
> > >>> 00010800  2**2
> > >>>                   CONTENTS, ALLOC, LOAD, READONLY, DATA
> > >>>   5 .bss          00001ec0  0000000140014000  0000000140014000  
> > >>> 00000000  2**4
> > >>>                   ALLOC
> > >>>   6 .idata        00000c88  0000000140016000  0000000140016000  
> > >>> 00011000  2**2
> > >>>                   CONTENTS, ALLOC, LOAD, DATA
> > >>>   7 .CRT          00000060  0000000140017000  0000000140017000  
> > >>> 00011e00  2**2
> > >>>                   CONTENTS, ALLOC, LOAD, DATA
> > >>>   8 .tls          00000010  0000000140018000  0000000140018000  
> > >>> 00012000  2**2
> > >>>                   CONTENTS, ALLOC, LOAD, DATA
> > >>>   9 .reloc        0000009c  0000000140019000  0000000140019000  
> > >>> 00012200  2**2
> > >>>                   CONTENTS, ALLOC, LOAD, READONLY, DATA
> > >>>  10 .debug_aranges 00000150  000000014001a000  000000014001a000  
> > >>> 00012400  2**0
> > >>>                   CONTENTS, READONLY, DEBUGGING
> > >>>  11 .debug_info   0000d5e4  000000014001b000  000000014001b000  
> > >>> 00012600  2**0
> > >>>                   CONTENTS, READONLY, DEBUGGING
> > >>>  12 .debug_abbrev 000014de  0000000140029000  0000000140029000  
> > >>> 0001fc00  2**0
> > >>>                   CONTENTS, READONLY, DEBUGGING
> > >>>  13 .debug_line   00001a36  000000014002b000  000000014002b000  
> > >>> 00021200  2**0
> > >>>                   CONTENTS, READONLY, DEBUGGING
> > >>>  14 .debug_frame  00000f40  000000014002d000  000000014002d000  
> > >>> 00022e00  2**0
> > >>>                   CONTENTS, READONLY, DEBUGGING
> > >>>  15 .debug_str    000003a0  000000014002e000  000000014002e000  
> > >>> 00023e00  2**0
> > >>>                   CONTENTS, READONLY, DEBUGGING
> > >>>  16 .debug_line_str 00000a76  000000014002f000  000000014002f000  
> > >>> 00024200  2**0
> > >>>                   CONTENTS, READONLY, DEBUGGING
> > >>>  17 .debug_loclists 0000174a  0000000140030000  0000000140030000  
> > >>> 00024e00  2**0
> > >>>                   CONTENTS, READONLY, DEBUGGING
> > >>>  18 .debug_rnglists 0000039c  0000000140032000  0000000140032000  
> > >>> 00026600  2**0
> > >>>                   CONTENTS, READONLY, DEBUGGING
> > >>
> > >> That's derived from libfd's internal representation, which means nothing 
> > >> at
> > >> all to the loader processing the image. If your objdump is suitably 
> > >> enabled,
> > >> try using its -P option.
> > >>
> > >> Jan
> > >
> > > You are right, I got
> > >
> > > Section headers (at offset 0x00000188):
> > >  # Name     paddr    vaddr    size     scnptr   relptr   lnnoptr   nrel 
> > > nlnno
> > >  1 .text    0000c7f8 00001000 0000c800 00000600 00000000 00000000     0   
> > >   0
> > >             Flags: 60000060: EXECUTE,READ,CODE,INITIALIZED DATA
> > >  2 .data    00000250 0000e000 00000400 0000ce00 00000000 00000000     0   
> > >   0
> > >             Flags: c0000040: READ,WRITE,INITIALIZED DATA
> > >  3 .rdata   00002c70 0000f000 00002e00 0000d200 00000000 00000000     0   
> > >   0
> > >             Flags: 40000040: READ,INITIALIZED DATA
> > >  4 .pdata   00000654 00012000 00000800 00010000 00000000 00000000     0   
> > >   0
> > >             Flags: 40000040: READ,INITIALIZED DATA
> > >  5 .xdata   00000630 00013000 00000800 00010800 00000000 00000000     0   
> > >   0
> > >             Flags: 40000040: READ,INITIALIZED DATA
> > >  6 .bss     00001ec0 00014000 00000000 00000000 00000000 00000000     0   
> > >   0
> > >             Flags: c0000080: READ,WRITE,UNINITIALIZED DATA
> > >  7 .idata   00000c88 00016000 00000e00 00011000 00000000 00000000     0   
> > >   0
> > >             Flags: c0000040: READ,WRITE,INITIALIZED DATA
> > >  8 .CRT     00000060 00017000 00000200 00011e00 00000000 00000000     0   
> > >   0
> > >             Flags: c0000040: READ,WRITE,INITIALIZED DATA
> > >  9 .tls     00000010 00018000 00000200 00012000 00000000 00000000     0   
> > >   0
> > >             Flags: c0000040: READ,WRITE,INITIALIZED DATA
> > > 10 .reloc   0000009c 00019000 00000200 00012200 00000000 00000000     0   
> > >   0
> > >             Flags: 42000040: DISCARDABLE,READ,INITIALIZED DATA
> > > 11 /4       00000150 0001a000 00000200 00012400 00000000 00000000     0   
> > >   0
> > >             Flags: 42000040: DISCARDABLE,READ,INITIALIZED DATA
> > > 12 /19      0000d5e4 0001b000 0000d600 00012600 00000000 00000000     0   
> > >   0
> > >             Flags: 42000040: DISCARDABLE,READ,INITIALIZED DATA
> > > 13 /31      000014de 00029000 00001600 0001fc00 00000000 00000000     0   
> > >   0
> > >             Flags: 42000040: DISCARDABLE,READ,INITIALIZED DATA
> > > 14 /45      00001a36 0002b000 00001c00 00021200 00000000 00000000     0   
> > >   0
> > >             Flags: 42000040: DISCARDABLE,READ,INITIALIZED DATA
> > > 15 /57      00000f40 0002d000 00001000 00022e00 00000000 00000000     0   
> > >   0
> > >             Flags: 42000040: DISCARDABLE,READ,INITIALIZED DATA
> > > 16 /70      000003a0 0002e000 00000400 00023e00 00000000 00000000     0   
> > >   0
> > >             Flags: 42000040: DISCARDABLE,READ,INITIALIZED DATA
> > > 17 /81      00000a76 0002f000 00000c00 00024200 00000000 00000000     0   
> > >   0
> > >             Flags: 42000040: DISCARDABLE,READ,INITIALIZED DATA
> > > 18 /97      0000174a 00030000 00001800 00024e00 00000000 00000000     0   
> > >   0
> > >             Flags: 42000040: DISCARDABLE,READ,INITIALIZED DATA
> > > 19 /113     0000039c 00032000 00000400 00026600 00000000 00000000     0   
> > >   0
> > >             Flags: 42000040: DISCARDABLE,READ,INITIALIZED DATA
> > >
> > > I suppose I will change to simply "Align some sections to 4KB"
> >
> > "Some" is imo going to be too imprecise. Please qualify which sections you
> > intend to align. If new sections need adding in the future, this then can
> > guide people as to whether those may also need aligning.
> >
> > Jan
> 
> The main issue is that sections with different permissions must be in
> separate sections.
> In the case of debug sections they are contiguous and have the same
> permissions so it's not an issue (although better to strip them off).
> 
> Any suggestions on how to describe this?

Maybe something like "Align sections of different permissions to force
them into separate pages"?

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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