git: c9501b977642 - stable/15 - powerpc: Fix alignment of initial PCB on kstack

The branch stable/15 has been updated by jhb:

URL: https://cgit.FreeBSD.org/src/commit/?id=c9501b97764246c59dcc5d3fb4cbaa54aea7e41e

commit c9501b97764246c59dcc5d3fb4cbaa54aea7e41e
Author:     John Baldwin <jhb@FreeBSD.org>
AuthorDate: 2026-01-27 18:30:46 +0000
Commit:     John Baldwin <jhb@FreeBSD.org>
CommitDate: 2026-04-24 15:26:39 +0000

    powerpc: Fix alignment of initial PCB on kstack
    
    Commit cc81c44dd806737f98b4fd4094674dd71c8749f3 aimed to consolidate
    duplicated code between the Book-E and AIM backends.  For
    cpu_thread_alloc cpu_thread_alloc and cpu_fork it used the AIM
    functions which used a bogus alignment mask (~0x2f).  The Book-E
    functions used a proper alignment mask (~0x3f).  The AIM functions
    appear to have been busted since they were first imported in commit
    919cb3362fded33aca682a6ac57777f8fff86e36.
    
    To fix, use the Book-E mask which requests 64 byte alignment.
    Probably this was harmless in practice since td_kstack is page aligned
    and struct pcb is probably a multiple of 32 bytes in size, so the 0x10
    bit should have been clear anyway.
    
    Reviewed by:    fuz, jhibbits
    Fixes:          cc81c44dd806 ("Unify ABI-related bits of the Book-E and AIM...")
    Effort:         CHERI upstreaming
    Sponsored by:   AFRL, DARPA
    Differential Revision:  https://reviews.freebsd.org/D54839
    (cherry picked from commit 9272b780626640ce9b9ac378fbdd2783aaa33625)
---
 sys/powerpc/powerpc/exec_machdep.c | 2 +-
 sys/powerpc/powerpc/vm_machdep.c   | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/sys/powerpc/powerpc/exec_machdep.c b/sys/powerpc/powerpc/exec_machdep.c
index 8a33d0f589a7..fde24370842e 100644
--- a/sys/powerpc/powerpc/exec_machdep.c
+++ b/sys/powerpc/powerpc/exec_machdep.c
@@ -1095,7 +1095,7 @@ cpu_thread_alloc(struct thread *td)
 	struct pcb *pcb;
 
 	pcb = (struct pcb *)((td->td_kstack + td->td_kstack_pages * PAGE_SIZE -
-	    sizeof(struct pcb)) & ~0x2fUL);
+	    sizeof(struct pcb)) & ~0x3fUL);
 	td->td_pcb = pcb;
 	td->td_frame = (struct trapframe *)pcb - 1;
 }
diff --git a/sys/powerpc/powerpc/vm_machdep.c b/sys/powerpc/powerpc/vm_machdep.c
index d47beedb595e..1fd853783cc8 100644
--- a/sys/powerpc/powerpc/vm_machdep.c
+++ b/sys/powerpc/powerpc/vm_machdep.c
@@ -124,7 +124,7 @@ cpu_fork(struct thread *td1, struct proc *p2, struct thread *td2, int flags)
 		cpu_update_pcb(td1);
 
 	pcb = (struct pcb *)((td2->td_kstack +
-	    td2->td_kstack_pages * PAGE_SIZE - sizeof(struct pcb)) & ~0x2fUL);
+	    td2->td_kstack_pages * PAGE_SIZE - sizeof(struct pcb)) & ~0x3fUL);
 	td2->td_pcb = pcb;
 
 	/* Copy the pcb */