[PATCH 0/2] lguest: Minor cleanups of boot code

[PATCH 0/2] lguest: Minor cleanups of boot code

[Paul Bolle]

Building arch/x86/lguest/boot.o triggers two warnings:
    arch/x86/lguest/boot.c: In function 'early_put_chars':
    arch/x86/lguest/boot.c:1300:5: warning: 'device_len' may be used uninitialized in this function [-Wmaybe-uninitialized]
      if (device_len < (offsetof(struct virtio_console_config, emerg_wr)
         ^
    arch/x86/lguest/boot.c:1238:6: note: 'device_len' was declared here
      u32 device_len;
          ^
    arch/x86/lguest/boot.c:1306:21: warning: 'device_offset' may be used uninitialized in this function [-Wmaybe-uninitialized]
      console_cfg_offset = device_offset;
                         ^
    arch/x86/lguest/boot.c:1237:6: note: 'device_offset' was declared here
      u32 device_offset;
          ^

These annoy me for some time now. So I investigated whether
probe_pci_console(), which actually triggers these warnings, could be
reorganized to make these warnings go away. (Because I really dislike to
initialize variables to some default value just to shut up the compiler.)

I came up with this short series. It makes, I think, the code clearer for the
people reading it. And as a bonus the compiler is silent now.

Paul Bolle (2):
  lguest: read length of device_cap later
  lguest: read offset of device_cap later

 arch/x86/lguest/boot.c | 17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

-- 
2.4.3

[PATCH 1/2] lguest: read length of device_cap later

[Paul Bolle]

Read the length of the capability with type VIRTIO_PCI_CAP_DEVICE_CFG
only when we're sure we're going to need it. Which is just before the
check whether the virtio console actually has an emerg_wr field.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
---
 arch/x86/lguest/boot.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c
index 4ba229ac3f4f..535e3197d0c7 100644
--- a/arch/x86/lguest/boot.c
+++ b/arch/x86/lguest/boot.c
@@ -1258,7 +1258,7 @@ static void probe_pci_console(void)
 		u8 vndr = read_pci_config_byte(0, 1, 0, cap);
 		if (vndr == PCI_CAP_ID_VNDR) {
 			u8 type, bar;
-			u32 offset, length;
+			u32 offset;
 
 			type = read_pci_config_byte(0, 1, 0,
 			    cap + offsetof(struct virtio_pci_cap, cfg_type));
@@ -1266,15 +1266,12 @@ static void probe_pci_console(void)
 			    cap + offsetof(struct virtio_pci_cap, bar));
 			offset = read_pci_config(0, 1, 0,
 			    cap + offsetof(struct virtio_pci_cap, offset));
-			length = read_pci_config(0, 1, 0,
-			    cap + offsetof(struct virtio_pci_cap, length));
 
 			switch (type) {
 			case VIRTIO_PCI_CAP_DEVICE_CFG:
 				if (bar == 0) {
 					device_cap = cap;
 					device_offset = offset;
-					device_len = length;
 				}
 				break;
 			case VIRTIO_PCI_CAP_PCI_CFG:
@@ -1297,6 +1294,8 @@ static void probe_pci_console(void)
 	 * emerg_wr.  If it doesn't support VIRTIO_CONSOLE_F_EMERG_WRITE
 	 * it should ignore the access.
 	 */
+	device_len = read_pci_config(0, 1, 0,
+			device_cap + offsetof(struct virtio_pci_cap, length));
 	if (device_len < (offsetof(struct virtio_console_config, emerg_wr)
 			  + sizeof(u32))) {
 		printk(KERN_ERR "lguest: console missing emerg_wr field\n");
-- 
2.4.3

[tip:x86/cleanups] lguest: Read length of device_cap later

[tip-bot for Paul Bolle]

Commit-ID:  7faf90ef995ea470f32f43810266ece8ac8ba6c7
Gitweb:     http://git.kernel.org/tip/7faf90ef995ea470f32f43810266ece8ac8ba6c7
Author:     Paul Bolle <pebolle@tiscali.nl>
AuthorDate: Thu, 3 Mar 2016 13:01:40 +0100
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 10 Jun 2016 11:39:09 +0200

lguest: Read length of device_cap later

Read the length of the capability with type VIRTIO_PCI_CAP_DEVICE_CFG
only when we're sure we're going to need it. Which is just before the
check whether the virtio console actually has an emerg_wr field.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: lguest@lists.ozlabs.org
Link: http://lkml.kernel.org/r/1457006501-5377-2-git-send-email-pebolle@tiscali.nl
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
 arch/x86/lguest/boot.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c
index 3847e73..146d11c 100644
--- a/arch/x86/lguest/boot.c
+++ b/arch/x86/lguest/boot.c
@@ -1258,7 +1258,7 @@ static void probe_pci_console(void)
 		u8 vndr = read_pci_config_byte(0, 1, 0, cap);
 		if (vndr == PCI_CAP_ID_VNDR) {
 			u8 type, bar;
-			u32 offset, length;
+			u32 offset;
 
 			type = read_pci_config_byte(0, 1, 0,
 			    cap + offsetof(struct virtio_pci_cap, cfg_type));
@@ -1266,15 +1266,12 @@ static void probe_pci_console(void)
 			    cap + offsetof(struct virtio_pci_cap, bar));
 			offset = read_pci_config(0, 1, 0,
 			    cap + offsetof(struct virtio_pci_cap, offset));
-			length = read_pci_config(0, 1, 0,
-			    cap + offsetof(struct virtio_pci_cap, length));
 
 			switch (type) {
 			case VIRTIO_PCI_CAP_DEVICE_CFG:
 				if (bar == 0) {
 					device_cap = cap;
 					device_offset = offset;
-					device_len = length;
 				}
 				break;
 			case VIRTIO_PCI_CAP_PCI_CFG:
@@ -1297,6 +1294,8 @@ static void probe_pci_console(void)
 	 * emerg_wr.  If it doesn't support VIRTIO_CONSOLE_F_EMERG_WRITE
 	 * it should ignore the access.
 	 */
+	device_len = read_pci_config(0, 1, 0,
+			device_cap + offsetof(struct virtio_pci_cap, length));
 	if (device_len < (offsetof(struct virtio_console_config, emerg_wr)
 			  + sizeof(u32))) {
 		printk(KERN_ERR "lguest: console missing emerg_wr field\n");

[PATCH 2/2] lguest: read offset of device_cap later

[Paul Bolle]

Read the offset of the capability with type VIRTIO_PCI_CAP_DEVICE_CFG
only when we're sure we're going to need it. Which is when all checks
have passed and we know we have a virtio console with an emerg_wr field.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
---
 arch/x86/lguest/boot.c | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c
index 535e3197d0c7..3b0c0eb4abf8 100644
--- a/arch/x86/lguest/boot.c
+++ b/arch/x86/lguest/boot.c
@@ -1233,8 +1233,6 @@ static void write_bar_via_cfg(u32 cfg_offset, u32 off, u32 val)
 static void probe_pci_console(void)
 {
 	u8 cap, common_cap = 0, device_cap = 0;
-	/* Offset within BAR0 */
-	u32 device_offset;
 	u32 device_len;
 
 	/* Avoid recursive printk into here. */
@@ -1258,21 +1256,16 @@ static void probe_pci_console(void)
 		u8 vndr = read_pci_config_byte(0, 1, 0, cap);
 		if (vndr == PCI_CAP_ID_VNDR) {
 			u8 type, bar;
-			u32 offset;
 
 			type = read_pci_config_byte(0, 1, 0,
 			    cap + offsetof(struct virtio_pci_cap, cfg_type));
 			bar = read_pci_config_byte(0, 1, 0,
 			    cap + offsetof(struct virtio_pci_cap, bar));
-			offset = read_pci_config(0, 1, 0,
-			    cap + offsetof(struct virtio_pci_cap, offset));
 
 			switch (type) {
 			case VIRTIO_PCI_CAP_DEVICE_CFG:
-				if (bar == 0) {
+				if (bar == 0)
 					device_cap = cap;
-					device_offset = offset;
-				}
 				break;
 			case VIRTIO_PCI_CAP_PCI_CFG:
 				console_access_cap = cap;
@@ -1302,7 +1295,8 @@ static void probe_pci_console(void)
 		return;
 	}
 
-	console_cfg_offset = device_offset;
+	console_cfg_offset = read_pci_config(0, 1, 0,
+			device_cap + offsetof(struct virtio_pci_cap, offset));
 	printk(KERN_INFO "lguest: Console via virtio-pci emerg_wr\n");
 }
 
-- 
2.4.3

[tip:x86/cleanups] lguest: Read offset of device_cap later

[tip-bot for Paul Bolle]

Commit-ID:  cf2cf0f50c14e86e04cda2c684357eed77922666
Gitweb:     http://git.kernel.org/tip/cf2cf0f50c14e86e04cda2c684357eed77922666
Author:     Paul Bolle <pebolle@tiscali.nl>
AuthorDate: Thu, 3 Mar 2016 13:01:41 +0100
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 10 Jun 2016 11:39:09 +0200

lguest: Read offset of device_cap later

Read the offset of the capability with type VIRTIO_PCI_CAP_DEVICE_CFG
only when we're sure we're going to need it. Which is when all checks
have passed and we know we have a virtio console with an emerg_wr field.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: lguest@lists.ozlabs.org
Link: http://lkml.kernel.org/r/1457006501-5377-3-git-send-email-pebolle@tiscali.nl
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
 arch/x86/lguest/boot.c | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c
index 146d11c..25da5bc8 100644
--- a/arch/x86/lguest/boot.c
+++ b/arch/x86/lguest/boot.c
@@ -1233,8 +1233,6 @@ static void write_bar_via_cfg(u32 cfg_offset, u32 off, u32 val)
 static void probe_pci_console(void)
 {
 	u8 cap, common_cap = 0, device_cap = 0;
-	/* Offset within BAR0 */
-	u32 device_offset;
 	u32 device_len;
 
 	/* Avoid recursive printk into here. */
@@ -1258,21 +1256,16 @@ static void probe_pci_console(void)
 		u8 vndr = read_pci_config_byte(0, 1, 0, cap);
 		if (vndr == PCI_CAP_ID_VNDR) {
 			u8 type, bar;
-			u32 offset;
 
 			type = read_pci_config_byte(0, 1, 0,
 			    cap + offsetof(struct virtio_pci_cap, cfg_type));
 			bar = read_pci_config_byte(0, 1, 0,
 			    cap + offsetof(struct virtio_pci_cap, bar));
-			offset = read_pci_config(0, 1, 0,
-			    cap + offsetof(struct virtio_pci_cap, offset));
 
 			switch (type) {
 			case VIRTIO_PCI_CAP_DEVICE_CFG:
-				if (bar == 0) {
+				if (bar == 0)
 					device_cap = cap;
-					device_offset = offset;
-				}
 				break;
 			case VIRTIO_PCI_CAP_PCI_CFG:
 				console_access_cap = cap;
@@ -1302,7 +1295,8 @@ static void probe_pci_console(void)
 		return;
 	}
 
-	console_cfg_offset = device_offset;
+	console_cfg_offset = read_pci_config(0, 1, 0,
+			device_cap + offsetof(struct virtio_pci_cap, offset));
 	printk(KERN_INFO "lguest: Console via virtio-pci emerg_wr\n");
 }