linux-kernel - [PATCH] x86/kernel: Mark expected switch fall-throughs

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Date:   Fri, 25 Jan 2019 12:39:03 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Kees Cook <keescook@...omium.org>
Subject: [PATCH] x86/kernel: Mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch
cases where we are expecting to fall through.

This patch fixes the following warnings:

arch/x86/kernel/hw_breakpoint.c:278:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
arch/x86/kernel/cpu/cacheinfo.c:250:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
arch/x86/kernel/kgdb.c:468:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
arch/x86/kernel/uprobes.c:747:8: warning: this statement may fall through [-Wimplicit-fallthrough=]
arch/x86/kernel/apic/io_apic.c: In function ‘irq_trigger’:
./include/linux/printk.h:305:2: warning: this statement may fall through [-Wimplicit-fallthrough=]
  printk(KERN_WARNING pr_fmt(fmt), ##__VA_ARGS__)
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/printk.h:306:17: note: in expansion of macro ‘pr_warning’
 #define pr_warn pr_warning
                 ^~~~~~~~~~
arch/x86/kernel/apic/io_apic.c:861:3: note: in expansion of macro ‘pr_warn’
   pr_warn("IOAPIC: Invalid trigger mode 2 defaulting to level\n");
   ^~~~~~~
arch/x86/kernel/apic/io_apic.c:862:2: note: here
  case MP_IRQTRIG_LEVEL:
  ^~~~
arch/x86/kernel/apic/io_apic.c: In function ‘irq_polarity’:
./include/linux/printk.h:305:2: warning: this statement may fall through [-Wimplicit-fallthrough=]
  printk(KERN_WARNING pr_fmt(fmt), ##__VA_ARGS__)
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/printk.h:306:17: note: in expansion of macro ‘pr_warning’
 #define pr_warn pr_warning
                 ^~~~~~~~~~
arch/x86/kernel/apic/io_apic.c:814:3: note: in expansion of macro ‘pr_warn’
   pr_warn("IOAPIC: Invalid polarity: 2, defaulting to low\n");
   ^~~~~~~
arch/x86/kernel/apic/io_apic.c:815:2: note: here
  case MP_IRQPOL_ACTIVE_LOW:
  ^~~~

Warning level 3 was used: -Wimplicit-fallthrough=3

This patch is part of the ongoing efforts to enabling -Wimplicit-fallthrough.

Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
---
 arch/x86/kernel/apic/io_apic.c  | 2 ++
 arch/x86/kernel/cpu/cacheinfo.c | 1 +
 arch/x86/kernel/hw_breakpoint.c | 1 +
 arch/x86/kernel/kgdb.c          | 1 +
 arch/x86/kernel/uprobes.c       | 1 +
 5 files changed, 6 insertions(+)

diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index 2953bbf05c08..264e3221d923 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -812,6 +812,7 @@ static int irq_polarity(int idx)
 		return IOAPIC_POL_HIGH;
 	case MP_IRQPOL_RESERVED:
 		pr_warn("IOAPIC: Invalid polarity: 2, defaulting to low\n");
+		/* fall through */
 	case MP_IRQPOL_ACTIVE_LOW:
 	default: /* Pointless default required due to do gcc stupidity */
 		return IOAPIC_POL_LOW;
@@ -859,6 +860,7 @@ static int irq_trigger(int idx)
 		return IOAPIC_EDGE;
 	case MP_IRQTRIG_RESERVED:
 		pr_warn("IOAPIC: Invalid trigger mode 2 defaulting to level\n");
+		/* fall through */
 	case MP_IRQTRIG_LEVEL:
 	default: /* Pointless default required due to do gcc stupidity */
 		return IOAPIC_LEVEL;
diff --git a/arch/x86/kernel/cpu/cacheinfo.c b/arch/x86/kernel/cpu/cacheinfo.c
index c4d1023fb0ab..395d46f78582 100644
--- a/arch/x86/kernel/cpu/cacheinfo.c
+++ b/arch/x86/kernel/cpu/cacheinfo.c
@@ -248,6 +248,7 @@ amd_cpuid4(int leaf, union _cpuid4_leaf_eax *eax,
 	switch (leaf) {
 	case 1:
 		l1 = &l1i;
+		/* fall through */
 	case 0:
 		if (!l1->val)
 			return;
diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
index 34a5c1715148..7d6f91f2869a 100644
--- a/arch/x86/kernel/hw_breakpoint.c
+++ b/arch/x86/kernel/hw_breakpoint.c
@@ -279,6 +279,7 @@ static int arch_build_bp_info(struct perf_event *bp,
 			hw->len = X86_BREAKPOINT_LEN_X;
 			return 0;
 		}
+		/* fall through */
 	default:
 		return -EINVAL;
 	}
diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index 5db08425063e..4ff6b4cdb941 100644
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -467,6 +467,7 @@ int kgdb_arch_handle_exception(int e_vector, int signo, int err_code,
 		ptr = &remcomInBuffer[1];
 		if (kgdb_hex2long(&ptr, &addr))
 			linux_regs->ip = addr;
+		/* fall through */
 	case 'D':
 	case 'k':
 		/* clear the trace bit */
diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 843feb94a950..ccf03416e434 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -745,6 +745,7 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
 		 * OPCODE1() of the "short" jmp which checks the same condition.
 		 */
 		opc1 = OPCODE2(insn) - 0x10;
+		/* fall through */
 	default:
 		if (!is_cond_jmp_opcode(opc1))
 			return -ENOSYS;
-- 
2.20.1