Re: [PATCH] libgloss: arm: Add hardfault handler for M-profile

I have sent an updated version as part of a new series (now 3 patches):
https://sourceware.org/pipermail/newlib/2026/022515.html

On 6/22/26 15:25, Christophe Lyon wrote:
> 
> 
> On 6/22/26 12:48, Richard Earnshaw wrote:
>> On 12/06/2026 16:53, Christophe Lyon wrote:
>>> After reaching a hardfault, the simulator enters an infinite loop
>>> unless we map the handler to 'abort'.
>>>
>>> The patch adds this minimal setup for M-profile in
>>> libgloss/arm/cpu-init/rdimon-aem.S and introduces the new
>>> libgloss/arm/elf-mprofile-mps2.specs to add the mapping to the right
>>> memory address.
>>>
>>> 2026-05-29  Andre Vieira <[email protected]>
>>>     Christophe Lyon  <[email protected]>
>>>
>>>     libgloss/
>>>     * Makefile.in: Add entry for arm/mprofile-mps2.specs.
>>>     * arm/Makefile.inc: Add entry for mprofile-mps2.specs.
>>>     * arm/cpu-init/rdimon-aem.S: Update comment. Add hardfault
>>>     handler.
>>>     * arm/elf-mprofile-mps2.specs: New file.
>>> ---
>>>   libgloss/Makefile.in                 |  1 +
>>>   libgloss/arm/Makefile.inc            |  3 ++-
>>>   libgloss/arm/cpu-init/rdimon-aem.S   | 11 +++++++++--
>>>   libgloss/arm/elf-mprofile-mps2.specs | 26 ++++++++++++++++++++++++++
>>>   4 files changed, 38 insertions(+), 3 deletions(-)
>>>   create mode 100644 libgloss/arm/elf-mprofile-mps2.specs
>>>
>>> diff --git a/libgloss/Makefile.in b/libgloss/Makefile.in
>>> index 5146a7880..c03ea4e6b 100644
>>> --- a/libgloss/Makefile.in
>>> +++ b/libgloss/Makefile.in
>>> @@ -2255,6 +2255,7 @@ TEXINFO_TEX = ../texinfo/texinfo.tex
>>>   @CONFIG_ARM_TRUE@    arm/aprofile-validation-v2m.specs \
>>>   @CONFIG_ARM_TRUE@    arm/aprofile-ve-v2m.specs \
>>>   @CONFIG_ARM_TRUE@    arm/aprofile-ve.specs arm/pid.specs \
>>> +@CONFIG_ARM_TRUE@       arm/mprofile-mps2.specs \
>>>   @CONFIG_ARM_TRUE@    arm/iq80310.specs
>>>   @CONFIG_ARM_TRUE@arm_libgloss_linux_a_SOURCES = \
>>>   @CONFIG_ARM_TRUE@    arm/linux-syscalls0.c \
>>> diff --git a/libgloss/arm/Makefile.inc b/libgloss/arm/Makefile.inc
>>> index 41fce3c99..5c740edcb 100644
>>> --- a/libgloss/arm/Makefile.inc
>>> +++ b/libgloss/arm/Makefile.inc
>>> @@ -47,7 +47,8 @@ multilibtool_LIBRARIES += %D%/librdpmon.a
>>>       %D%/aprofile-validation.specs \
>>>       %D%/aprofile-validation-v2m.specs \
>>>       %D%/aprofile-ve-v2m.specs \
>>> -    %D%/aprofile-ve.specs
>>> +    %D%/aprofile-ve.specs \
>>> +    %D%/mprofile-mps2.specs
>>>   multilibtool_DATA += \
>>>       %D%/rdimon-crt0.o \
>>>       %D%/rdimon-crt0-v2m.o
>>> diff --git a/libgloss/arm/cpu-init/rdimon-aem.S b/libgloss/arm/cpu- 
>>> init/rdimon-aem.S
>>> index 2aacbeba9..c960924d4 100644
>>> --- a/libgloss/arm/cpu-init/rdimon-aem.S
>>> +++ b/libgloss/arm/cpu-init/rdimon-aem.S
>> It looks to me as though there's no shared code in this file compared 
>> to the a-profile variant, which makes me think that perhaps they 
>> should just be separate files, rather than munged together when 
>> there's no commonality beyond 'this is startup code'.
>  > > Personally, I think it would be better to rename the existing file as
>> something like rdimon-aem-a.S and then add a new one (say, rdimon-aem- 
>> m.S) for the m-profile code.
>>
> Indeed, before this patch the code is specific to A-profile, and this 
> patch adds a section dedicated to M-profile (no nothing common with A- 
> profile).
> I think having 2 files makes sense but seems tricky to handle at 
> Makefile level (wrt multilibs).
> So maybe:
> - rename rdi-mon-aem.S into rdimon-aem-a.S, and re-create rdi-mon-aem.S 
> which only includes rdimon-aem-a.S
> - add rdimon-aem-m.S and make rdi-mon-aem.S include it unconditionally
> 
> This way we have 2 separate source files, but no change to the build 
> system and multilib support
> 
> 
>>> @@ -25,7 +25,9 @@
>>>   /* This file gives a basic initialisation of a Cortex-A series 
>>> core.  It is
>>>      the bare minimum required to get Cortex-A core running with a 
>>> semihosting
>>> -   interface.
>>> +   interface.  For M-profile we only define a hardfault handler, 
>>> required to
>>> +   prevent the simulator from entering into an infinite loop.  The 
>>> comments
>>> +   below apply to A-profile only.
>>
>> If I've missed something and this code does belong in this file, then 
>> this whole comment needs properly restructuring.  There should be a 
>> single top-level comment that just says something like "Provide the 
>> basic CPU initialization for Armv7 and later CPUs.  We currently 
>> support A-profile and M-profile.  Then the profile-specific details 
>> should be moved inside the relevant ifdef sections.  It would be good 
>> to get rid of the reference to 'Cortex-A' here as well (replace it 
>> with A-profile) as there's nothing here that is specific to Arm's 
>> Cortex-* products: this is defined by the architecture.
> 
> If I move rdimon-aem.S into rdimon-aem-a.S, I can probably make some 
> small adjustments to this comment (and not add mentions of M-profile). 
> This comment has been unmodified since ... 2013!
>>
>> Finally, if you're keeping this in one place, the copyright dates at 
>> the top of the file need updating.
>>
>>>      It sets up a basic 1:1 phsyical address to virtual address mapping;
>>>      turns the MMU on; enables branch prediction; activates any 
>>> integrated
>>> @@ -539,4 +541,9 @@ is_a15_a7:
>>>   page_tables:
>>>        PT7(0x1c0e)
>>> -#endif //#if defined(__ARM_ARCH_7A__) || __ARM_ARCH_PROFILE == 'A'
>>> +#elif  (__ARM_ARCH_PROFILE == 'M')
>>> +    /* On M-profile, call abort in case of hardfault: this causes 
>>> the simulator to
>>> +       abort execution instead of going into an infinite loop.  */
>>> +    .section .hardfault_handler_addr, "a"
>>> +    .word abort
>>> +#endif //#if defined(__ARM_ARCH_7A__) || (__ARM_ARCH_PROFILE == 'A')
>>> diff --git a/libgloss/arm/elf-mprofile-mps2.specs b/libgloss/arm/elf- 
>>> mprofile-mps2.specs
>>> new file mode 100644
>>> index 000000000..edaf71917
>>> --- /dev/null
>>> +++ b/libgloss/arm/elf-mprofile-mps2.specs
>>> @@ -0,0 +1,26 @@
>>> +# rdimon.specs
>>> +#
>>> +# Spec file for AArch32 M profile baremetal newlib with version 2 of
>>> +# the AngelAPI semi-hosting using the SVC trap instruction.
>>> +#
>>> +# This version supports extensibility through an extension mechanism.
>>> +
>>> +%rename link_gcc_c_sequence                rdimon_link_gcc_c_sequence
>>> +
>>> +%rename link old_link
>>> +
>>> +*link:
>>> +--section-start=.hardfault_handler_addr=0xc %(old_link)
>>> +
>>> +*rdimon_libc:
>>> +%{!specs=nano.specs:-lc} %{specs=nano.specs:-lc_nano}
>>> +
>>> +*rdimon_libgloss:
>>> +%{!specs=nano.specs:-lrdimon} %{specs=nano.specs:-lrdimon_nano}
>>> +
>>> +*link_gcc_c_sequence:
>>> +%(rdimon_link_gcc_c_sequence) --start-group %G %(rdimon_libc) 
>>> %(rdimon_libgloss) --end-group
>>> +
>>> +*startfile:
>>> +crti%O%s crtbegin%O%s cpu-init/rdimon-aem.o%s %{!pg:rdimon-crt0%O%s} 
>>> %{pg:rdimon-crt0%O%s}
>>> +
>>
>