[cadcdev-svn-commits] [SCM] branch master updated. b4c45a947548022020173b1621efe4fe6a9ccb71

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- Log -----------------------------------------------------------------
commit b4c45a947548022020173b1621efe4fe6a9ccb71
Author: Paul Cercueil <pa...@cr...>
Date:   Wed May 21 12:23:59 2025 +0200

    environ: Switch to gUSA atomic model
    
    Switch to the gUSA atomic model, which allows atomics to work without
    having to mask interrupts.
    
    Signed-off-by: Paul Cercueil <pa...@cr...>

commit a42a8a5d84142ebd92825bd889c59bb3179a9db1
Author: Paul Cercueil <pa...@cr...>
Date:   Sun May 19 13:33:46 2024 +0200

    Add support for gUSA atomic model
    
    Add support for the gUSA atomic model, which is what is used in the
    Linux kernel. By specifying -matomic-model=soft-gusa, the gUSA atomic
    model can now be used.
    
    Instead of creating critical sections by masking interrupts, gUSA relies
    on the scheduler detecting atomic sections, identified by the stack
    pointer going negative, and rolling back to the beginning of the atomic
    section if interrupted in the middle.
    
    The minimal overhead added to the scheduler is balanced by the gains
    recovered by not masking interrupts for every single atomic access.
    
    Signed-off-by: Paul Cercueil <pa...@cr...>

-----------------------------------------------------------------------

Summary of changes:
 environ_dreamcast.sh               |  2 +-
 kernel/arch/dreamcast/kernel/irq.c | 10 ++++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/environ_dreamcast.sh b/environ_dreamcast.sh
index 7dd3e872..e947323b 100644
--- a/environ_dreamcast.sh
+++ b/environ_dreamcast.sh
@@ -24,7 +24,7 @@ if [ -z "${KOS_SH4_PRECISION}" ] || [ "${KOS_SH4_PRECISION}" = "-m4-single" ]; t
     fi
 fi
 
-export KOS_CFLAGS="${KOS_CFLAGS} ${KOS_SH4_PRECISION} -ml -mfsrra -mfsca -ffunction-sections -fdata-sections -matomic-model=soft-imask -ftls-model=local-exec"
+export KOS_CFLAGS="${KOS_CFLAGS} ${KOS_SH4_PRECISION} -ml -mfsrra -mfsca -ffunction-sections -fdata-sections -matomic-model=soft-gusa -ftls-model=local-exec"
 export KOS_AFLAGS="${KOS_AFLAGS} -little"
 export KOS_LDFLAGS="${KOS_LDFLAGS} ${KOS_SH4_PRECISION} -ml -Wl,--gc-sections"
 export KOS_LD_SCRIPT="-T${KOS_BASE}/utils/ldscripts/shlelf.xc"
diff --git a/kernel/arch/dreamcast/kernel/irq.c b/kernel/arch/dreamcast/kernel/irq.c
index c8a23011..3e3be5a8 100644
--- a/kernel/arch/dreamcast/kernel/irq.c
+++ b/kernel/arch/dreamcast/kernel/irq.c
@@ -216,6 +216,16 @@ void irq_handle_exception(int code) {
     uint32_t evt = 0;
     int handled = 0;
 
+    if(__is_defined(__SH_ATOMIC_MODEL_SOFT_GUSA__)
+       && __unlikely((int32_t)irq_srt_addr->r[15] >= -128
+                     && irq_srt_addr->pc != irq_srt_addr->r[0])) {
+        /* The stack pointer has been altered: it means we are in the middle of
+           an atomic section, and we need to roll-back.
+           The r0 register contains the address of the end of the section,
+           and the stack pointer contains the negated section size. */
+        irq_srt_addr->pc = irq_srt_addr->r[0] + irq_srt_addr->r[15];
+    }
+
     switch(code) {
         /* If it's a code 3, grab the event from intevt. */
         case 3:


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A pseudo Operating System for the Dreamcast.