[Patch 3/8, Arm, GCC] Add option -mbranch-protection. [Was RE: [Patch 2/7, Arm, GCC] Add option -mbranch-protection.]

[Tejas Belagod <Tejas.Belagod@arm.com>]

[-- Attachment #1: Type: text/plain, Size: 2452 bytes --]



> -----Original Message-----
> From: Richard Earnshaw <Richard.Earnshaw@arm.com>
> Sent: Monday, October 11, 2021 1:58 PM
> To: Tejas Belagod <Tejas.Belagod@arm.com>; gcc-patches@gcc.gnu.org
> Subject: Re: [Patch 2/7, Arm, GCC] Add option -mbranch-protection.
> 
> On 08/10/2021 13:17, Tejas Belagod via Gcc-patches wrote:
> > Hi,
> >
> > Add -mbranch-protection option and its associated parsing routines.
> > This option enables the code-generation of pointer signing and
> > authentication instructions in function prologues and epilogues.
> >
> > Tested on arm-none-eabi. OK for trunk?
> >
> > 2021-10-04  Tejas Belagod  <tbelagod@arm.com>
> >
> > gcc/ChangeLog:
> >
> > 	* common/config/arm/arm-common.c
> > 	 (arm_print_hit_for_pacbti_option): New.
> > 	 (arm_progress_next_token): New.
> > 	 (arm_parse_pac_ret_clause): New routine for parsing the
> > 	pac-ret clause for -mbranch-protection.
> > 	(arm_parse_pacbti_option): New routine to parse all the options
> > 	to -mbranch-protection.
> > 	* config/arm/arm-protos.h (arm_parse_pacbti_option): Export.
> > 	* config/arm/arm.c (arm_configure)build_target): Handle option
> > 	to -mbranch-protection.
> > 	* config/arm/arm.opt (mbranch-protection). New.
> > 	(arm_enable_pacbti): New.
> >
> 
> You're missing documentation for invoke.texi.
> 
> Also, how does this differ from the exising option in aarch64?  Can the code
> from that be adapted to be made common to both targets rather than doing
> a new implementation?
> 
> Finally, there are far to many manifest constants in this patch, they need
> replacing with enums or #defines as appropriate if we cannot share the
> aarch64 code.

Thanks for the reviews.

Add -mbranch-protection option.  This option enables the code-generation of
pointer signing and authentication instructions in function prologues and
epilogues.

2021-10-25  Tejas Belagod  <tbelagod@arm.com>

gcc/ChangeLog:

	* config/arm/arm.c (arm_configure_build_target): Parse and validate
	-mbranch-protection option and initialize appropriate data structures.
	* config/arm/arm.opt: New option -mbranch-protection.
	* doc/invoke.texi: Document -mbranch-protection.

Tested the following configurations, OK for trunk?

-mthumb/-march=armv8.1-m.main+pacbti/-mfloat-abi=soft
-marm/-march=armv7-a/-mfpu=vfpv3-d16/-mfloat-abi=softfp
mcmodel=small and tiny
aarch64-none-linux-gnu native test and bootstrap


[-- Attachment #2: mbranch_prot.txt --]
[-- Type: text/plain, Size: 3006 bytes --]

diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index a952655db80663f28f5a5d12005f2adb4702894f..946841526ee127105396097d143e755bdfc756f5 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -3216,6 +3216,17 @@ arm_configure_build_target (struct arm_build_target *target,
       tune_opts = strchr (opts->x_arm_tune_string, '+');
     }
 
+  if (opts->x_arm_branch_protection_string)
+    {
+      aarch_validate_mbranch_protection (opts->x_arm_branch_protection_string);
+
+      if (aarch_ra_sign_key != AARCH_KEY_A)
+	{
+	  warning (0, "invalid key type for %<-mbranch-protection=%>");
+	  aarch_ra_sign_key = AARCH_KEY_A;
+	}
+    }
+
   if (arm_selected_arch)
     {
       arm_initialize_isa (target->isa, arm_selected_arch->common.isa_bits);
diff --git a/gcc/config/arm/arm.opt b/gcc/config/arm/arm.opt
index 5c5b4f3ae0699a3a9d78df40a5ab65324dcba7b9..4f2754c3e84c436f7058ea0bd1c9f517b3a63ccd 100644
--- a/gcc/config/arm/arm.opt
+++ b/gcc/config/arm/arm.opt
@@ -313,6 +313,10 @@ mbranch-cost=
 Target RejectNegative Joined UInteger Var(arm_branch_cost) Init(-1)
 Cost to assume for a branch insn.
 
+mbranch-protection=
+Target RejectNegative Joined Var(arm_branch_protection_string) Save
+Use branch-protection features.
+
 mgeneral-regs-only
 Target RejectNegative Mask(GENERAL_REGS_ONLY) Save
 Generate code which uses the core registers only (r0-r14).
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 27df8cf5bee79c2abac8b81c1ac54f1c3e50c628..7f886db008a39c44819616eb2799c01822d0aae9 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -810,7 +810,9 @@ Objective-C and Objective-C++ Dialects}.
 -mpure-code @gol
 -mcmse @gol
 -mfix-cmse-cve-2021-35465 @gol
--mfdpic}
+-mfdpic @gol
+-mbranch-protection=@var{none}|@var{standard}|@var{pac-ret}[+@var{leaf}]
+[+@var{bti}]|@var{bti}[+@var{pac-ret}[+@var{leaf}]]}
 
 @emph{AVR Options}
 @gccoptlist{-mmcu=@var{mcu}  -mabsdata  -maccumulate-args @gol
@@ -20969,6 +20971,18 @@ The opposite @option{-mno-fdpic} option is useful (and required) to
 build the Linux kernel using the same (@code{arm-*-uclinuxfdpiceabi})
 toolchain as the one used to build the userland programs.
 
+@item -mbranch-protection=@var{none}|@var{standard}|@var{pac-ret}[+@var{leaf}][+@var{bti}]|@var{bti}[+@var{pac-ret}[+@var{leaf}]]
+@opindex mbranch-protection
+Select the branch protection features to use.
+@samp{none} is the default and turns off all types of branch protection.
+@samp{standard} turns on all types of branch protection features.  If a feature
+has additional tuning options, then @samp{standard} sets it to its standard
+level.
+@samp{pac-ret[+@var{leaf}]} turns on return address signing to its standard
+level: signing functions that save the return address to memory (non-leaf
+functions will practically always do this).  The optional argument @samp{leaf}
+can be used to extend the signing to include leaf functions.
+@samp{bti} turns on branch target identification mechanism.
 @end table
 
 @node AVR Options